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Luiz Belardinelli - One of the best experts on this subject based on the ideXlab platform.
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pharmacology and therapeutic applications of a1 adenosine Receptor ligands
Current Topics in Medicinal Chemistry, 2003Co-Authors: Arvinder K Dhalla, John C Shryock, Revati Shreeniwas, Luiz BelardinelliAbstract:Adenosines diverse physiological functions are mediated by four subtypes of Receptors (A1, A2A, A2B and A3). The A1 adenosine Receptor pharmacology and therapeutic application of ligands for this Receptor are the subjects of this review. A1 Receptors are present on the surface of cells in organs throughout the body. Actions mediated by A1 Receptors include slowing of heart rate and AV nodal conduction, reduction of atrial contractility, attenuation of the stimulatory actions of catecholamines on beta-adrenergic Receptors, reduction of lipolysis in adipose tissue, reduction of urine formation, and inhibition of neuronal activity. Although adenosine analogs with high efficacy, affinity, and selectivity for the A1 Receptor are available, the ubiquitous distribution and wide range of physiological actions mediated by A1 Receptors are obstacles to development of therapeutic agents that activate these Receptors. However, it may be possible to exploit the high A1 “Receptor Reserve” for some actions of adenosine by use of weak (partial) agonists to target these actions while avoiding others for which Receptor Reserve is low. The presence of high Receptor Reserves for the anti-arrhythmic and anti-lipolytic actions of adenosine suggests that partial A1 agonists could be used as anti-arrhythmic and anti-lipolytic agents. In addition, allosteric enhancers of the binding of adenosine to A1 Receptors could be used therapeutically to potentiate desirable effects of endogenous adenosine. Antagonists of the A1 Receptor can increase urine formation, and because they do not decrease renal blood flow, are particularly useful to maintain glomerular filtration in patients having edema secondary to reduced cardiac function.
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novel short acting a2a adenosine Receptor agonists for coronary vasodilation inverse relationship between affinity and duration of action of a2a agonists
Journal of Pharmacology and Experimental Therapeutics, 2001Co-Authors: Zhenhai Gao, Stephen P Baker, Robert D Lasley, S Meyer, Elfatih Elzein, Venkata Palle, Jeff Zablocki, Brent Blackburn, Luiz BelardinelliAbstract:Several potent and selective A2A adenosine Receptor agonists are currently available. These compounds have a high affinity for the A2A Receptor and a long duration of action. However, in situations where a short duration of action is desired, currently available A2A Receptor agonists are less than ideal. From a series of recently synthesized A2A Receptor agonists, two agonists (CVT-3146 and CVT-3033) with low affinity were selected for further characterization as selective and short-acting coronary vasodilators. Both compounds were selective for the A2A adenosine Receptor (AdoR) versus the A1, A2B, and A3AdoR in binding and functional studies. CVT-3146 and CVT-3033 appeared to be weak partial agonists to cause cAMP accumulation in PC12 cells, but were full and potent agonists to cause coronary vasodilation, a response that has a very large A2A Receptor Reserve. However, the durations of action of CVT-3146 and CVT-3033 were remarkably shorter than those of the high-affinity agonists CGS21680 or WRC0470, presumably due to the relative lower affinity of CVT-3146 and CVT-3033 for the A2A Receptor. Indeed, an inverse relationship was found between the affinity of the various agonists for the A2AReceptor and the duration of their actions. These data indicate that low-affinity agonists can produce a response that is of equivalent magnitude but more rapid in termination than that caused by a high-affinity agonist. Hence, the low-affinity A2A agonists CVT-3146 and CVT-3033 may prove to be superior to currently available high-affinity agonists as coronary vasodilators during myocardial imaging with radionuclide agents.
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differential a1 adenosine Receptor Reserve for inhibition of cyclic amp accumulation and g protein activation in ddt1 mf 2 cells
British Journal of Pharmacology, 2000Co-Authors: Stephen P Baker, Peter J Scammells, Luiz BelardinelliAbstract:The A1-adenosine Receptor (A1AdoR) Reserve for N6-cyclopentyladenosine (CPA) mediated inhibition of (−)isoprenaline stimulated cyclic AMP accumulation and stimulation of [35S]-guanosine-5′-O-(thiotriphosphate) (GTPγS) binding, a measure of guanine nucleotide binding protein (G-protein) activation, was determined in DDT1 MF-2 cells. Inactivation of the A1AdoRs with the chemoreactive ligand 8-cyclopentyl-3-[3-[[4-(fluorosulphonyl)benzoyl]oxy]propyl]-1-propylxanthine (FSCPX) caused a progressive rightward shift of the concentration-response curves for CPA to inhibit cyclic AMP accumulation, with a maximum of 10 fold increase in the EC50 value. In contrast, inactivation of A1AdoR's caused only a 1.7 fold rightward shift in the CPA concentration-response for stimulation of [35S]-GTPγS binding. The A1AdoR occupancy-response relationship for CPA inhibition of cyclic AMP accumulation was hyperbolic with 43% Receptor occupancy required to elicit the maximal response, i.e. a 57% A1AdoR Reserve. In contrast, the A1AdoR occupancy-response relationship for CPA mediated stimulation of [35S]-GTPγS binding was linear indicating little or no Receptor Reserve for G-protein activation. The relationship between CPA stimulation of [35S]-GTPγS binding and cyclic AMP inhibition was also hyperbolic with 44% G-protein activation sufficient to cause maximal inhibition. The data suggest that the A1AdoR Reserve for CPA mediated inhibition of cyclic AMP accumulation occurs at the level of G-protein interaction with adenylyl cyclase. However, each A1AdoR appears to activate a constant fraction of the total G-protein population suggesting signal amplification at the Receptor-G-protein level which may also contribute to the Receptor Reserve for CPA. British Journal of Pharmacology (2000) 130, 1156–1164; doi:10.1038/sj.bjp.0703405
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a2a adenosine Receptor Reserve for coronary vasodilation
Circulation, 1998Co-Authors: John C Shryock, Stephen P Baker, Stephen Snowdy, Pier Giovanni Baraldi, Barbara Cacciari, Giampiero Spalluto, Angela Monopoli, Ennio Ongini, Luiz BelardinelliAbstract:Background—Adenosine is a potent coronary vasodilator and causes an increase of coronary blood flow by activation of A2A-adenosine Receptors (A2A-AdoRs). The purpose of this study was to test the hypothesis that the high potency of adenosine and adenosine analogues to cause coronary vasodilation is explained by the presence of a large A2A-AdoR Reserve (“spare Receptors”). Methods and Results—A novel, irreversible antagonist of A2A-AdoRs was used to inactivate Receptors and reduce the response to agonist. Agonist-induced increases of coronary conductance before and after exposure of hearts to the irreversible antagonist were compared. Three agonists were studied: 2-p-(2-carboxyethyl)-phenethylamino-5′-N-ethylcarboxamidoadenosine (CGS21680), adenosine, and 2-chloro-N6-cyclopentyladenosine (CCPA). Data were analyzed to determine agonist KA (equilibrium dissociation constant) and EC50 values. Values of KA for activation of A2A-AdoRs by CGS21680, adenosine, and CCPA were 105, 1800, and 2630 nmol/L, respectivel...
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validation of furchgott s method to determine agonist dependent a1 adenosine Receptor Reserve in guinea pig atrium
British Journal of Pharmacology, 1998Co-Authors: Timothy E Morey, Luiz Belardinelli, Donn M DennisAbstract:1. The ubiquitous distribution of A1-adenosine Receptors (A1AdoR) represents an impediment to achieve organ and/or response selectivity of A1AdoR agonists. Differential Receptor Reserve may be exploited to overcome this problem. We hypothesize that A1AdoR Reserve is agonist-dependent and can be accurately estimated with Furchgott's method. 2. Concentration-response curves were constructed from measurement of the atrial monophasic action potential duration in guinea-pig, isolated hearts treated with R(-) N6-(2-phenylisopropyl)adenosine (R-PIA) or 2-chloro-N6-cyclopentyl-adenosine (CCPA) before and after treatment with the selective, irreversible A1AdoR antagonist 8-cyclopentyl-3-[3-[[4-(fluorosulphonyl)benzoyl]oxy]propyl]-1-prop ylxanthine (FSCPX). Using Furchgott's method, we determined the equilibrium dissociation constant (KA) of R-PIA and CCPA, and the fraction of non-inactivated A1AdoRs remaining after FSCPX treatment (q(functional)). Values of q(functional) were correlated to the fraction of specific binding sites after FSCPX treatment labelled by [3H]-8-cyclopentyl-1,3-dipropylxanthine ([3H]-CPX) derived from saturation binding normalized to control (q(binding)). 3. Both R-PIA and CCPA are full A1AdoR agonists, but have significantly different potencies (pD2 [EC50]=6.84+/-0.04 [145 nM] vs 7.36+/-0.04 [44 nM], respectively), Receptor affinities (pKA [KA]= 6.54+/-0.10 [288 nM] vs 6.13+/-0.03 [734 nM]), and pharmacological shift ratios defined as KA/EC50 (2.2+/-0.6 vs 15.9+/-1.5). Values for q(functional) and q(binding) were highly correlated (r2=0.96). The ratio between the intrinsic efficacies of CCPA and R-PIA derived from Furchgott's analysis was 5.9, a value similar to the ratio of 6.2-6.6 calculated from previously obtained binding data. 4. Radioligand binding studies validated the use of Furchgott's method to estimate A1AdoR Reserve. A1AdoR Reserve was agonist-dependent. CCPA was shown to be a high intrinsic efficacy, low affinity agonist, whereas R-PIA was found to be a low intrinsic efficacy, high affinity agonist.
Stephen P Baker - One of the best experts on this subject based on the ideXlab platform.
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novel short acting a2a adenosine Receptor agonists for coronary vasodilation inverse relationship between affinity and duration of action of a2a agonists
Journal of Pharmacology and Experimental Therapeutics, 2001Co-Authors: Zhenhai Gao, Stephen P Baker, Robert D Lasley, S Meyer, Elfatih Elzein, Venkata Palle, Jeff Zablocki, Brent Blackburn, Luiz BelardinelliAbstract:Several potent and selective A2A adenosine Receptor agonists are currently available. These compounds have a high affinity for the A2A Receptor and a long duration of action. However, in situations where a short duration of action is desired, currently available A2A Receptor agonists are less than ideal. From a series of recently synthesized A2A Receptor agonists, two agonists (CVT-3146 and CVT-3033) with low affinity were selected for further characterization as selective and short-acting coronary vasodilators. Both compounds were selective for the A2A adenosine Receptor (AdoR) versus the A1, A2B, and A3AdoR in binding and functional studies. CVT-3146 and CVT-3033 appeared to be weak partial agonists to cause cAMP accumulation in PC12 cells, but were full and potent agonists to cause coronary vasodilation, a response that has a very large A2A Receptor Reserve. However, the durations of action of CVT-3146 and CVT-3033 were remarkably shorter than those of the high-affinity agonists CGS21680 or WRC0470, presumably due to the relative lower affinity of CVT-3146 and CVT-3033 for the A2A Receptor. Indeed, an inverse relationship was found between the affinity of the various agonists for the A2AReceptor and the duration of their actions. These data indicate that low-affinity agonists can produce a response that is of equivalent magnitude but more rapid in termination than that caused by a high-affinity agonist. Hence, the low-affinity A2A agonists CVT-3146 and CVT-3033 may prove to be superior to currently available high-affinity agonists as coronary vasodilators during myocardial imaging with radionuclide agents.
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differential a1 adenosine Receptor Reserve for inhibition of cyclic amp accumulation and g protein activation in ddt1 mf 2 cells
British Journal of Pharmacology, 2000Co-Authors: Stephen P Baker, Peter J Scammells, Luiz BelardinelliAbstract:The A1-adenosine Receptor (A1AdoR) Reserve for N6-cyclopentyladenosine (CPA) mediated inhibition of (−)isoprenaline stimulated cyclic AMP accumulation and stimulation of [35S]-guanosine-5′-O-(thiotriphosphate) (GTPγS) binding, a measure of guanine nucleotide binding protein (G-protein) activation, was determined in DDT1 MF-2 cells. Inactivation of the A1AdoRs with the chemoreactive ligand 8-cyclopentyl-3-[3-[[4-(fluorosulphonyl)benzoyl]oxy]propyl]-1-propylxanthine (FSCPX) caused a progressive rightward shift of the concentration-response curves for CPA to inhibit cyclic AMP accumulation, with a maximum of 10 fold increase in the EC50 value. In contrast, inactivation of A1AdoR's caused only a 1.7 fold rightward shift in the CPA concentration-response for stimulation of [35S]-GTPγS binding. The A1AdoR occupancy-response relationship for CPA inhibition of cyclic AMP accumulation was hyperbolic with 43% Receptor occupancy required to elicit the maximal response, i.e. a 57% A1AdoR Reserve. In contrast, the A1AdoR occupancy-response relationship for CPA mediated stimulation of [35S]-GTPγS binding was linear indicating little or no Receptor Reserve for G-protein activation. The relationship between CPA stimulation of [35S]-GTPγS binding and cyclic AMP inhibition was also hyperbolic with 44% G-protein activation sufficient to cause maximal inhibition. The data suggest that the A1AdoR Reserve for CPA mediated inhibition of cyclic AMP accumulation occurs at the level of G-protein interaction with adenylyl cyclase. However, each A1AdoR appears to activate a constant fraction of the total G-protein population suggesting signal amplification at the Receptor-G-protein level which may also contribute to the Receptor Reserve for CPA. British Journal of Pharmacology (2000) 130, 1156–1164; doi:10.1038/sj.bjp.0703405
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a2a adenosine Receptor Reserve for coronary vasodilation
Circulation, 1998Co-Authors: John C Shryock, Stephen P Baker, Stephen Snowdy, Pier Giovanni Baraldi, Barbara Cacciari, Giampiero Spalluto, Angela Monopoli, Ennio Ongini, Luiz BelardinelliAbstract:Background—Adenosine is a potent coronary vasodilator and causes an increase of coronary blood flow by activation of A2A-adenosine Receptors (A2A-AdoRs). The purpose of this study was to test the hypothesis that the high potency of adenosine and adenosine analogues to cause coronary vasodilation is explained by the presence of a large A2A-AdoR Reserve (“spare Receptors”). Methods and Results—A novel, irreversible antagonist of A2A-AdoRs was used to inactivate Receptors and reduce the response to agonist. Agonist-induced increases of coronary conductance before and after exposure of hearts to the irreversible antagonist were compared. Three agonists were studied: 2-p-(2-carboxyethyl)-phenethylamino-5′-N-ethylcarboxamidoadenosine (CGS21680), adenosine, and 2-chloro-N6-cyclopentyladenosine (CCPA). Data were analyzed to determine agonist KA (equilibrium dissociation constant) and EC50 values. Values of KA for activation of A2A-AdoRs by CGS21680, adenosine, and CCPA were 105, 1800, and 2630 nmol/L, respectivel...
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differential a1 adenosine Receptor Reserve for two actions of adenosine on guinea pig atrial myocytes
Molecular Pharmacology, 1997Co-Authors: Miduturu Srinivas, Stephen P Baker, John C Shryock, Donn M Dennis, Luiz BelardinelliAbstract:Adenosine activates adenosine-induced inwardly rectifying K+ current (IKAdo) and inhibits isoproterenol (100 nM)-stimulated L-type Ca2+ current (beta-ICa,L) of guinea pig atrial myocytes with EC50 values of 2.17 and 0.20 microM, respectively. We determined whether this 11-fold difference in potency of adenosine is due to the existence of a greater A1 adenosine Receptor Reserve for the inhibition of beta-ICa,L than for the activation of IKAdo. Atrial myocytes were pretreated with vehicle (control) or the irreversible A1 adenosine Receptor antagonist 8-cyclopentyl-3-[3-[[4-(fluorosulfonyl)benzoyl]oxy]propyl]-1-propylxa nthine (FSCPX) (10 and 50 nM) for 30 min, and after a 60-min washout period, concentration-response curves were determined for the adenosine-induced activation of IKAdo and inhibition of beta-ICa,L. Pretreatment of atrial myocytes with 10 nM FSCPX reduced the maximal activation of IKAdo by 60% (7.9 +/- 0.2 to 3.2 +/- 0.1 pA/pF). In contrast, a higher concentration of FSCPX (50 nM) was required to reduce the maximal inhibition of beta-ICa,L by 39% (95 +/- 4% to 58. 7 +/- 5.6%) and caused a 15-fold increase in the EC50 value of adenosine. Values of the equilibrium dissociation constant (KA) for adenosine to activate IKAdo and inhibit beta-ICa,L, estimated according to the method of Furchgott, were 2.7 and 5.6 microM, respectively. These values were used to determine the relationship between adenosine Receptor occupancy and response. Half-maximal and maximal activations of IKAdo required occupancies of 40% and 98% of A1 adenosine Receptors, respectively. In contrast, occupancies of only 4% and 70%, respectively, of A1 adenosine Receptors were sufficient to cause half-maximal and maximal inhibitions of beta-ICa, L. Consistent with this result, a partial agonist of the A1 adenosine Receptor SHA040 inhibited beta-ICa,L by 60 +/- 3.5% but activated IKAdo by only 18.1 +/- 2.5%. The results indicate that the A1 adenosine Receptor is coupled more efficiently to an inhibition of beta-ICa,L than to an activation of IKAdo.
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persistent activation by and Receptor Reserve for an irreversible a1 adenosine Receptor agonist in ddt1 mf 2 cells and in guinea pig heart
Molecular Pharmacology, 1997Co-Authors: Jiahui Zhang, Luiz Belardinelli, Kenneth A Jacobson, Deborah H Otero, Stephen P BakerAbstract:The p - and m -isothiocyanate adenosine derivatives N 6 -[4-[[[4-[[[[2-[[[( p -( m )-isothiocyanatophenyl)amino]thiocarbonyl]amino]ethyl]amino]carbonyl]methyl]anilino]carbonyl]methyl]phenyl]adenosine ( p - and m -DITC-ADAC) were examined for irreversible agonist effects at the A 1 -adenosine Receptor (A 1 -AdoR) in DDT 1 MF-2 (DDT) cells and a functional A 1 -AdoR response in the guinea pig isolated heart. The p - and m -DITC-ADAC inhibited (−)-isoproterenol stimulated cAMP accumulation in DDT cells in the low nanomolar range, and the maximal responses elicited by both compounds were similar to that for N 6 -cyclopentyladenosine. Once established, the p -DITC-ADAC-mediated inhibition of cAMP accumulation in DDT cells was not affected by the addition of the AdoR antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX). Pretreatment of DDT cells with p -DITC-ADAC (1 μm), followed by washing, reduced [ 3 H]CPX binding to the A 1 -AdoR by 44% without altering the K d value for the radioligand to the remaining Receptors. The relationship between irreversible A 1 -AdoR occupancy by p -DITC-ADAC and inhibition of cAMP accumulation revealed a relatively large Receptor Reserve (64%) for the maximal response. In guinea pig isolated hearts, m -DITC-ADAC (5 μm) prolonged the stimulus to His bundle (SH) interval by 2.1-fold; this response could be prevented by the antagonist 8-cyclopentyltheophylline (5 μm). However, after the SH interval prolongation was established, extensive washout or the addition of 8-cyclopentyltheophylline had little reversal effect on the m -DITC-ADAC response. Binding of [ 3 H]CPX to the guinea pig ventricular membranes after m -DITC-ADAC treatment and washing was reduced by 35%. The A 1 -AdoR occupancy response relationship for m -DITC-ADAC to prolong the SH interval indicated a small (10–20%) Receptor Reserve. Both p -and m -DITC-ADAC seem to be irreversible full agonists at the A 1 -AdoR and may prove to be useful probes to further investigate A 1 -AdoR structure-function relationships.
John C Shryock - One of the best experts on this subject based on the ideXlab platform.
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pharmacology and therapeutic applications of a1 adenosine Receptor ligands
Current Topics in Medicinal Chemistry, 2003Co-Authors: Arvinder K Dhalla, John C Shryock, Revati Shreeniwas, Luiz BelardinelliAbstract:Adenosines diverse physiological functions are mediated by four subtypes of Receptors (A1, A2A, A2B and A3). The A1 adenosine Receptor pharmacology and therapeutic application of ligands for this Receptor are the subjects of this review. A1 Receptors are present on the surface of cells in organs throughout the body. Actions mediated by A1 Receptors include slowing of heart rate and AV nodal conduction, reduction of atrial contractility, attenuation of the stimulatory actions of catecholamines on beta-adrenergic Receptors, reduction of lipolysis in adipose tissue, reduction of urine formation, and inhibition of neuronal activity. Although adenosine analogs with high efficacy, affinity, and selectivity for the A1 Receptor are available, the ubiquitous distribution and wide range of physiological actions mediated by A1 Receptors are obstacles to development of therapeutic agents that activate these Receptors. However, it may be possible to exploit the high A1 “Receptor Reserve” for some actions of adenosine by use of weak (partial) agonists to target these actions while avoiding others for which Receptor Reserve is low. The presence of high Receptor Reserves for the anti-arrhythmic and anti-lipolytic actions of adenosine suggests that partial A1 agonists could be used as anti-arrhythmic and anti-lipolytic agents. In addition, allosteric enhancers of the binding of adenosine to A1 Receptors could be used therapeutically to potentiate desirable effects of endogenous adenosine. Antagonists of the A1 Receptor can increase urine formation, and because they do not decrease renal blood flow, are particularly useful to maintain glomerular filtration in patients having edema secondary to reduced cardiac function.
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a2a adenosine Receptor Reserve for coronary vasodilation
Circulation, 1998Co-Authors: John C Shryock, Stephen P Baker, Stephen Snowdy, Pier Giovanni Baraldi, Barbara Cacciari, Giampiero Spalluto, Angela Monopoli, Ennio Ongini, Luiz BelardinelliAbstract:Background—Adenosine is a potent coronary vasodilator and causes an increase of coronary blood flow by activation of A2A-adenosine Receptors (A2A-AdoRs). The purpose of this study was to test the hypothesis that the high potency of adenosine and adenosine analogues to cause coronary vasodilation is explained by the presence of a large A2A-AdoR Reserve (“spare Receptors”). Methods and Results—A novel, irreversible antagonist of A2A-AdoRs was used to inactivate Receptors and reduce the response to agonist. Agonist-induced increases of coronary conductance before and after exposure of hearts to the irreversible antagonist were compared. Three agonists were studied: 2-p-(2-carboxyethyl)-phenethylamino-5′-N-ethylcarboxamidoadenosine (CGS21680), adenosine, and 2-chloro-N6-cyclopentyladenosine (CCPA). Data were analyzed to determine agonist KA (equilibrium dissociation constant) and EC50 values. Values of KA for activation of A2A-AdoRs by CGS21680, adenosine, and CCPA were 105, 1800, and 2630 nmol/L, respectivel...
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differential a1 adenosine Receptor Reserve for two actions of adenosine on guinea pig atrial myocytes
Molecular Pharmacology, 1997Co-Authors: Miduturu Srinivas, Stephen P Baker, John C Shryock, Donn M Dennis, Luiz BelardinelliAbstract:Adenosine activates adenosine-induced inwardly rectifying K+ current (IKAdo) and inhibits isoproterenol (100 nM)-stimulated L-type Ca2+ current (beta-ICa,L) of guinea pig atrial myocytes with EC50 values of 2.17 and 0.20 microM, respectively. We determined whether this 11-fold difference in potency of adenosine is due to the existence of a greater A1 adenosine Receptor Reserve for the inhibition of beta-ICa,L than for the activation of IKAdo. Atrial myocytes were pretreated with vehicle (control) or the irreversible A1 adenosine Receptor antagonist 8-cyclopentyl-3-[3-[[4-(fluorosulfonyl)benzoyl]oxy]propyl]-1-propylxa nthine (FSCPX) (10 and 50 nM) for 30 min, and after a 60-min washout period, concentration-response curves were determined for the adenosine-induced activation of IKAdo and inhibition of beta-ICa,L. Pretreatment of atrial myocytes with 10 nM FSCPX reduced the maximal activation of IKAdo by 60% (7.9 +/- 0.2 to 3.2 +/- 0.1 pA/pF). In contrast, a higher concentration of FSCPX (50 nM) was required to reduce the maximal inhibition of beta-ICa,L by 39% (95 +/- 4% to 58. 7 +/- 5.6%) and caused a 15-fold increase in the EC50 value of adenosine. Values of the equilibrium dissociation constant (KA) for adenosine to activate IKAdo and inhibit beta-ICa,L, estimated according to the method of Furchgott, were 2.7 and 5.6 microM, respectively. These values were used to determine the relationship between adenosine Receptor occupancy and response. Half-maximal and maximal activations of IKAdo required occupancies of 40% and 98% of A1 adenosine Receptors, respectively. In contrast, occupancies of only 4% and 70%, respectively, of A1 adenosine Receptors were sufficient to cause half-maximal and maximal inhibitions of beta-ICa, L. Consistent with this result, a partial agonist of the A1 adenosine Receptor SHA040 inhibited beta-ICa,L by 60 +/- 3.5% but activated IKAdo by only 18.1 +/- 2.5%. The results indicate that the A1 adenosine Receptor is coupled more efficiently to an inhibition of beta-ICa,L than to an activation of IKAdo.
Rudolf Gesztelyi - One of the best experts on this subject based on the ideXlab platform.
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methodical challenges and a possible resolution in the assessment of Receptor Reserve for adenosine an agonist with short half life
Molecules, 2017Co-Authors: Judit Zsuga, Tamas Erdei, Katalin Szabo, Nora Lampe, Csaba Papp, Akos Pinter, A J Szentmiklosi, Bela Juhasz, Zoltan Szilvassy, Rudolf GesztelyiAbstract:The term Receptor Reserve, first introduced and used in the traditional Receptor theory, is an integrative measure of response-inducing ability of the interaction between an agonist and a Receptor system (consisting of a Receptor and its downstream signaling). The underlying phenomenon, i.e., stimulation of a submaximal fraction of Receptors can apparently elicit the maximal effect (in certain cases), provides an opportunity to assess the Receptor Reserve. However, determining Receptor Reserve is challenging for agonists with short half-lives, such as adenosine. Although adenosine metabolism can be inhibited several ways (in order to prevent the rapid elimination of adenosine administered to construct concentration–effect (E/c) curves for the determination), the consequent accumulation of endogenous adenosine biases the results. To address this problem, we previously proposed a method, by means of which this bias can be mathematically corrected (utilizing a traditional Receptor theory-independent approach). In the present investigation, we have offered in silico validation of this method by simulating E/c curves with the use of the operational model of agonism and then by evaluating them using our method. We have found that our method is suitable to reliably assess the Receptor Reserve for adenosine in our recently published experimental setting, suggesting that it may be capable for a qualitative determination of Receptor Reserve for rapidly eliminating agonists in general. In addition, we have disclosed a possible interference between FSCPX (8-cyclopentyl-N3-[3-(4-(fluorosulfonyl)benzoyloxy)propyl]-N1-propylxanthine), an irreversible A1 adenosine Receptor antagonist, and NBTI (S-(2-hydroxy-5-nitrobenzyl)-6-thioinosine), a nucleoside transport inhibitor, i.e., FSCPX may blunt the effect of NBTI.
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approximation of a1 adenosine Receptor Reserve appertaining to the direct negative inotropic effect of adenosine in hyperthyroid guinea pig left atria
General Physiology and Biophysics, 2014Co-Authors: Krisztian Pak, Csaba Papp, A J Szentmiklosi, Bela Juhasz, Zoltan Galajda, Tamas Szerafin, Balazs Varga, David D Haines, Arpad Tosaki, Rudolf GesztelyiAbstract:Hyperthyroidism elevates cardiovascular mortality by several mechanisms, including increased risk of ischemic heart disease. Therefore, therapeutic strategies, which enhance tolerance of heart to ischemia-reperfusion injury, may be particularly useful for hyperthyroid patients. One promising cardioprotective approach is use of agents that cause (directly or indirectly) A1 adenosine Receptor (A1 Receptor) activation, since A1 adenosinergic pathways initiate protective mechanisms such as ischemic preconditioning. However, previously we found great A1 Receptor Reserve for the direct negative inotropic effect of adenosine in isolated guinea pig atria. This phenomenon suggests that weakening of atria is a possible side effect of A1 adenosinergic stimulant agents. Thus, the goal of the present investigation was to explore this Receptor Reserve in hyperthyroidism. Our recently developed method was used that prevents the rapid intracellular elimination of adenosine, allowing sufficient time for exogenous adenosine administered for the generation of concentration-response curves to exert its effect. Our method also allowed correction for the bias caused by the consequent endogenous adenosine accumulation. Our results demonstrate that thyroxine treatment does not substantially affect the A1 Receptor Reserve for the direct negative inotropic effect of adenosine. Consequently, if an agent causing A1 Receptor activation is administered for any indication, the most probable adverse effect affecting the heart may be a decrease of atrial contractility in both eu- and hyperthyroid conditions.
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the guinea pig atrial a1 adenosine Receptor Reserve for the direct negative inotropic effect of adenosine
General Physiology and Biophysics, 2014Co-Authors: Zsuzsanna Kiss, Judit Zsuga, A J Szentmiklosi, Bela Juhasz, Krisztian Pak, Balazs Varga, David D Haines, Arpad Tosaki, Rudolf GesztelyiAbstract:Although the A1 adenosine Receptor (A1 Receptor), the main adenosine Receptor type in cardiac muscle, is involved in powerful cardioprotective processes such as ischemic preconditioning, the atrial A1 Receptor Reserve has not yet been quantified for the direct negative inotropic effect of adenosine. In the present study, adenosine concentration-effect (E/c) curves were constructed before and after pretreatment with FSCPX (8-cyclopentyl-N3-[3-(4-(fluorosulfonyl)benzoyloxy)propyl]-N1-propylxanthine), an irreversible A1 Receptor antagonist, in isolated guinea pig atria. To prevent the intracellular elimination of the administered adenosine, NBTI (S-(2-hydroxy-5-nitrobenzyl)-6-thioinosine), a nucleoside transport inhibitor, was used. As expected, NBTI alone and FSCPX-pretreatment alone shifted the adenosine E/c curve to the left and right, respectively. However, in the presence of NBTI, FSCPX-pretreatment appeared to increase the maximal response to adenosine. By means of the Receptorial responsiveness method (RRM), our recently developed procedure, adenosine E/c curves generated in the presence of NBTI were corrected for the bias caused by the endogenous adenosine accumulated by NBTI. The corrected curves indicate a substantial A1 Receptor Reserve for the direct negative inotropy evoked by adenosine. In addition, our results suggest that accumulation of an endogenous agonist may bias the E/c curve constructed with the same or similar agonist that can lead to seemingly paradoxical results.
Donn M Dennis - One of the best experts on this subject based on the ideXlab platform.
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validation of furchgott s method to determine agonist dependent a1 adenosine Receptor Reserve in guinea pig atrium
British Journal of Pharmacology, 1998Co-Authors: Timothy E Morey, Luiz Belardinelli, Donn M DennisAbstract:1. The ubiquitous distribution of A1-adenosine Receptors (A1AdoR) represents an impediment to achieve organ and/or response selectivity of A1AdoR agonists. Differential Receptor Reserve may be exploited to overcome this problem. We hypothesize that A1AdoR Reserve is agonist-dependent and can be accurately estimated with Furchgott's method. 2. Concentration-response curves were constructed from measurement of the atrial monophasic action potential duration in guinea-pig, isolated hearts treated with R(-) N6-(2-phenylisopropyl)adenosine (R-PIA) or 2-chloro-N6-cyclopentyl-adenosine (CCPA) before and after treatment with the selective, irreversible A1AdoR antagonist 8-cyclopentyl-3-[3-[[4-(fluorosulphonyl)benzoyl]oxy]propyl]-1-prop ylxanthine (FSCPX). Using Furchgott's method, we determined the equilibrium dissociation constant (KA) of R-PIA and CCPA, and the fraction of non-inactivated A1AdoRs remaining after FSCPX treatment (q(functional)). Values of q(functional) were correlated to the fraction of specific binding sites after FSCPX treatment labelled by [3H]-8-cyclopentyl-1,3-dipropylxanthine ([3H]-CPX) derived from saturation binding normalized to control (q(binding)). 3. Both R-PIA and CCPA are full A1AdoR agonists, but have significantly different potencies (pD2 [EC50]=6.84+/-0.04 [145 nM] vs 7.36+/-0.04 [44 nM], respectively), Receptor affinities (pKA [KA]= 6.54+/-0.10 [288 nM] vs 6.13+/-0.03 [734 nM]), and pharmacological shift ratios defined as KA/EC50 (2.2+/-0.6 vs 15.9+/-1.5). Values for q(functional) and q(binding) were highly correlated (r2=0.96). The ratio between the intrinsic efficacies of CCPA and R-PIA derived from Furchgott's analysis was 5.9, a value similar to the ratio of 6.2-6.6 calculated from previously obtained binding data. 4. Radioligand binding studies validated the use of Furchgott's method to estimate A1AdoR Reserve. A1AdoR Reserve was agonist-dependent. CCPA was shown to be a high intrinsic efficacy, low affinity agonist, whereas R-PIA was found to be a low intrinsic efficacy, high affinity agonist.
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differential a1 adenosine Receptor Reserve for two actions of adenosine on guinea pig atrial myocytes
Molecular Pharmacology, 1997Co-Authors: Miduturu Srinivas, Stephen P Baker, John C Shryock, Donn M Dennis, Luiz BelardinelliAbstract:Adenosine activates adenosine-induced inwardly rectifying K+ current (IKAdo) and inhibits isoproterenol (100 nM)-stimulated L-type Ca2+ current (beta-ICa,L) of guinea pig atrial myocytes with EC50 values of 2.17 and 0.20 microM, respectively. We determined whether this 11-fold difference in potency of adenosine is due to the existence of a greater A1 adenosine Receptor Reserve for the inhibition of beta-ICa,L than for the activation of IKAdo. Atrial myocytes were pretreated with vehicle (control) or the irreversible A1 adenosine Receptor antagonist 8-cyclopentyl-3-[3-[[4-(fluorosulfonyl)benzoyl]oxy]propyl]-1-propylxa nthine (FSCPX) (10 and 50 nM) for 30 min, and after a 60-min washout period, concentration-response curves were determined for the adenosine-induced activation of IKAdo and inhibition of beta-ICa,L. Pretreatment of atrial myocytes with 10 nM FSCPX reduced the maximal activation of IKAdo by 60% (7.9 +/- 0.2 to 3.2 +/- 0.1 pA/pF). In contrast, a higher concentration of FSCPX (50 nM) was required to reduce the maximal inhibition of beta-ICa,L by 39% (95 +/- 4% to 58. 7 +/- 5.6%) and caused a 15-fold increase in the EC50 value of adenosine. Values of the equilibrium dissociation constant (KA) for adenosine to activate IKAdo and inhibit beta-ICa,L, estimated according to the method of Furchgott, were 2.7 and 5.6 microM, respectively. These values were used to determine the relationship between adenosine Receptor occupancy and response. Half-maximal and maximal activations of IKAdo required occupancies of 40% and 98% of A1 adenosine Receptors, respectively. In contrast, occupancies of only 4% and 70%, respectively, of A1 adenosine Receptors were sufficient to cause half-maximal and maximal inhibitions of beta-ICa, L. Consistent with this result, a partial agonist of the A1 adenosine Receptor SHA040 inhibited beta-ICa,L by 60 +/- 3.5% but activated IKAdo by only 18.1 +/- 2.5%. The results indicate that the A1 adenosine Receptor is coupled more efficiently to an inhibition of beta-ICa,L than to an activation of IKAdo.
