Iberiotoxin

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Ah Weston - One of the best experts on this subject based on the ideXlab platform.

  • stimulated release of a hyperpolarizing factor adhf from mesenteric artery perivascular adipose tissue involvement of myocyte bkca channels and adiponectin
    British Journal of Pharmacology, 2013
    Co-Authors: Ah Weston, Iris Egner, Y Dong, E L Porter, A M Heagerty, Gillian Edwards
    Abstract:

    Background and Purpose Perivascular adipose tissue (PVAT) releases adipocyte-derived hyperpolarizing factors (ADHFs) that may partly act by opening myocyte K+ channels. The present study in rat and mouse mesenteric arteries aimed to identify the myocyte K+ channel activated by PVAT and to determine whether adiponectin contributed to the hyperpolarizing effects of PVAT. Experimental Approach Myocyte membrane potential was recorded from de-endothelialized, non-contracted rat and mouse mesenteric arteries in the presence and absence of PVAT. Key Results The β3-adrenoceptor agonist, CL-316,243 (10 μM), generated PVAT-dependent, Iberiotoxin-sensitive myocyte hyperpolarizations resulting from BKCa channel opening and which were partially blocked by L-NMMA (100 μM). Adiponectin (5 μg·mL−1) also produced Iberiotoxin-sensitive hyperpolarizations in PVAT-denuded arterioles. Activation of myocyte AMP-activated protein kinase (AMPK) using 5 μM A-769662 also induced BKCa-mediated hyperpolarizations. Dorsomorphin abolished hyperpolarizations to CL-316,243, adiponectin and A-769662. In vessels from Adipo−/− mice, hyperpolarizations to CL-316,243 were absent whereas those to A-769662 and adiponectin were normal. In rat vessels, adipocyte-dependent hyperpolarizations were blocked by glibenclamide and clotrimazole but those to NS1619 (33 μM) were unaltered. Conclusions and Implications Under basal, non-contracted conditions, β3-adrenoceptor stimulation of PVAT releases an ADHF, which is probably adiponectin. This activates AMPK to open myocyte BKCa channels indirectly and additionally liberates NO, which also contributes to the observed PVAT-dependent myocyte hyperpolarizations. Clotrimazole and glibenclamide each reversed hyperpolarizations to adiponectin and A-769662, suggesting the involvement of myocyte TRPM4 channels in the ADHF-induced myocyte electrical changes mediated via the opening of BKCa channels.

  • characterization of a charybdotoxin sensitive intermediate conductance ca2 activated k channel in porcine coronary endothelium relevance to edhf
    British Journal of Pharmacology, 2002
    Co-Authors: Rostislav Bychkov, Ah Weston, M P Burnham, Gillian R Richards, Gillian Edwards, Michel Feletou, Paul M Vanhoutte
    Abstract:

    This study characterizes the K+ channel(s) underlying charybdotoxin-sensitive hyperpolarization of porcine coronary artery endothelium. Two forms of current-voltage (I/V) relationship were evident in whole-cell patch-clamp recordings of freshly-isolated endothelial cells. In both cell types, Iberiotoxin (100 nM) inhibited a current active only at potentials over +50 mV. In the presence of Iberiotoxin, charybdotoxin (100 nM) produced a large inhibition in 38% of cells and altered the form of the I/V relationship. In the remaining cells, charybdotoxin also inhibited a current but did not alter the form. Single-channel, outside-out patch recordings revealed a 17.1±0.4 pS conductance. Pipette solutions containing 100, 250 and 500 nM free Ca2+ demonstrated that the open probability was increased by Ca2+. This channel was blocked by charybdotoxin but not by Iberiotoxin or apamin. Hyperpolarizations of intact endothelium elicited by substance P (100 nM; 26.1±0.7 mV) were reduced by apamin (100 nM; 17.0±1.8 mV) whereas those to 1-ethyl-2-benzimidazolinone (1-EBIO, 600 μM, 21.0±0.3 mV) were unaffected (21.7±0.8 mV). Substance P, bradykinin (100 nM) and 1-EBIO evoked charybdotoxin-sensitive, Iberiotoxin-insensitive whole-cell perforated-patch currents. A porcine homologue of the intermediate-conductance Ca2+-activated K+ channel (IK1) was identified in endothelial cells. In conclusion, porcine coronary artery endothelial cells express an intermediate-conductance Ca2+-activated K+ channel and the IK1 gene product. This channel is opened by activation of the EDHF pathway and likely mediates the charybdotoxin-sensitive component of the EDHF response. Keywords: Endothelium, EDHF, hyperpolarization, calcium-activated potassium channels, charybdotoxin, Iberiotoxin, apamin, IK1 gene product Introduction The vascular endothelium controls vessel tone by releasing nitric oxide (Furchgott & Zawadzki, 1980) and prostacyclin (Moncada & Vane, 1979) as well as by a third pathway which involves hyperpolarization of the vascular smooth muscle (reviewed by Busse et al., 2002). This ‘endothelium-dependent hyperpolarizing factor (EDHF)' pathway is inhibited by a combination of the toxins apamin and charybdotoxin, but not apamin and Iberiotoxin (Corriu et al., 1996; Zygmunt & Hogestatt, 1996; Petersson et al., 1997; Chataigneau et al., 1998; Edwards et al., 1998; 2000). Given the specificities of these toxins (reviewed by Garcia et al., 1991; Castle, 1999), small- and intermediate-conductance Ca2+-activated K+ channels (SKCa and IKCa, respectively) but not large-conductance Ca2+-activated K+ channels (BKCa) are implicated in the EDHF pathway. In the vasculature, SKCa and IKCa are expressed in endothelial cells (Sakai, 1990; Marchenko & Sage, 1996; Kohler et al., 2000; Burnham et al., 2002) but not in smooth muscle cells with the contractile phenotype while BKCa are mainly expressed in myocytes (Zygmunt et al., 1997; Neylon et al., 1999; Quignard et al., 2000). Furthermore, the combination of apamin and charybdotoxin blocks EDHF-mediated vasodilatation if selectively applied to the endothelium and inhibits the hyperpolarization of the endothelial cells produced by acetylcholine or bradykinin (Edwards et al., 1998; 2000; Doughty et al., 1999; Ohashi et al., 1999). Finally, the increase in endothelial intracellular calcium concentration, provoked by the agonist, is not inhibited by the two toxins (Ghisdal & Morel, 2001). Altogether, these experimental results suggest that the hyperpolarization of the endothelial cells is the critical initiating step in the EDHF-mediated responses (Quignard et al., 2000; Edwards et al., 2000; Busse et al., 2002) and that apamin plus charybdotoxin exert their effects at this site (Edwards et al., 1998). In an earlier study, in porcine coronary artery endothelial cells, an apamin-sensitive K+ channel which is likely to be involved in the EDHF response was proposed to be an SKCa containing the SK3 subunit (Burnham et al., 2002). The purpose of the present study was, in the same cells, to characterize the K+ channels sensitive to charybdotoxin which are also involved in EDHF-mediated responses.

  • 3-Morpholinosydnonimine (SIN-1) and K+ channels in smooth muscle cells of the rabbit and guinea pig carotid arteries
    'Elsevier BV', 2000
    Co-Authors: Jf Quignard, Félétou M, Corriu C, Chataigneau T, Edwards G, Ah Weston, Pm Vanhoutte
    Abstract:

    Experiments were designed to determine the subtype of K+ channels activated by the nitrovasodilator 3-morpholinosydnonimine (SIN-1) in smooth muscle cells of the rabbit and guinea pig carotid arteries. Membrane potential was recorded in isolated segments with intracellular microelectrode and K+ currents in freshly dissociated smooth muscle cells, with the patch-clamp technique. In the guinea pig carotid artery, SIN-1 caused a glibenclamide-sensitive hyperpolarization. The nitrovasodilator did not affect the whole-cell K+ current, but activated a glibenclamide-sensitive K+ current. In the rabbit carotid artery, SIN-1 induced only an Iberiotoxin-sensitive repolarization in phenylephrine-depolarized tissue and in isolated cells, enhanced the activity of an Iberiotoxin-sensitive K+ current. These findings demonstrate that the population of K+ channels activated by nitric oxide (NO) is species-dependent and support the conclusion that, in the guinea pig carotid artery, in contrast to the rabbit carotid artery, the release of NO cannot account for the responses attributed to endothelium-derived hyperpolarizing factor (EDHF). Copyright (C) 2000 Elsevier Science B.V.link_to_subscribed_fulltex

  • further investigation of endothelium derived hyperpolarizing factor edhf in rat hepatic artery studies using 1 ebio and ouabain
    British Journal of Pharmacology, 1999
    Co-Authors: Gerald E Edwards, M J Gardener, Michel Feletou, Paul M Vanhoutte, G Brady, Ah Weston
    Abstract:

    The characteristics of endothelium-dependent hyperpolarization in rat hepatic artery have been further investigated in the presence of inhibitors of cyclo-oxygenase and nitric oxide synthase. Using sharp micro-electrodes, the smooth muscle hyperpolarization induced by acetylcholine, KCl or 1-ethyl-2-benzimidazolinone (1-EBIO) in intact hepatic arteries was abolished by 30 μM barium plus 500 nM ouabain. In vessels without endothelium, the smooth muscle hyperpolarization induced by KCl was not reduced by 30 μM barium alone. However, in the presence of barium the effects of KCl were partially inhibited by 100 nM ouabain and essentially abolished by 500 nM ouabain. Using sharp micro-electrodes, the hyperpolarization of both the smooth muscle and the endothelium induced by 1-EBIO or by acetylcholine was unaffected by 100 nM Iberiotoxin. However, in the presence of 100 nM charybdotoxin, the effects of 1-EBIO were abolished whereas those of acetylcholine were only partially reduced. The hyperpolarization induced by levcromakalim was unaffected by either charybdotoxin or Iberiotoxin. Under whole-cell patch-clamp recording conditions, 1-EBIO induced a voltage-insensitive, charybdotoxin-sensitive K+ current in cultured endothelial cells but was without effect on K+ currents in smooth muscle cells isolated from hepatic arteries. It is concluded that the endothelium-dependent hyperpolarization of smooth muscle induced by either acetylcholine or by 1-EBIO in rat hepatic artery is initially associated with the opening of endothelial calcium-sensitive K+-channels insensitive to Iberiotoxin. The resulting accumulation of K+ in the myoendothelial space activates an isoform of Na+/K+-ATPase which is sensitive to low concentrations of ouabain. British Journal of Pharmacology (1999) 128, 1064–1070; doi:10.1038/sj.bjp.0702916

Elizabeth E Sugg - One of the best experts on this subject based on the ideXlab platform.

  • synthetic charybdotoxin Iberiotoxin chimeric peptides define toxin binding sites on calcium activated and voltage dependent potassium channels
    Biochemistry, 1993
    Co-Authors: Kathleen M Giangiacomo, Elizabeth E Sugg, Owen B Mcmanus, Margarita Garciacalvo, Reid J Leonard, Gregory J Kaczorowski, Maria L Garcia
    Abstract:

    Charybdotoxin (ChTX) and Iberiotoxin (IbTX) are highly charged peptidyl toxins which exhibit 68% sequence identity and share a similar three-dimensional structure. Despite these structural similarities, IbTX and ChTX differ in their selectivity for two types of potassium channels; large conductance calcium-activated potassium (maxi-K) channels and slowly inactivating voltage-gated (Kv1.3) potassium channels. ChTX blocks with high affinity both maxi-K and Kv1.3 channels, while IbTX blocks the maxi-K but not the voltage-gated channel. To identify regions of the toxins which impart this this selectivity, we have constructed by solid-phase synthesis two chimeric toxins, ChTX1-19IbTX20-37 (Ch-IbTX) and IbTX1-19ChTX20-37 (Ib-ChTX), as well as a truncated peptide, ChTX7-37. These peptides were assayed for their ability to inhibit [125I]ChTX binding in sarcolemmal vesicles from smooth muscle (maxi-K binding) and [125I]ChTX binding to plasma membranes from brain (Kv1.3 binding). The ability of the peptides to block the maxi-K channel was determined from recordings of single maxi-K channels incorporated into planar lipid bilayers. Block of Kv1.3 was determined from recordings of whole cell currents in Xenopus oocytes injected with mRNA encoding the cloned Kv1.3 channel. Both chimeric toxins inhibited [125I]ChTX binding to sarcolemmal membranes from smooth muscle, and they both blocked the maxi-K channel in planar lipid bilayers. In contrast, [125I]ChTX binding in brain and Kv1.3 currents expressed in oocytes were inhibited only by the chimera Ib-ChTX.(ABSTRACT TRUNCATED AT 250 WORDS)

  • determination of the three dimensional structure of Iberiotoxin in solution by 1h nuclear magnetic resonance spectroscopy
    Biochemistry, 1992
    Co-Authors: Bruce A Johnson, Elizabeth E Sugg
    Abstract:

    The solution structure of chemically synthesized Iberiotoxin, a scorpion toxin that blocks Ca(2+)-activated K+ channels, has been determined using 2D 1H NMR spectroscopy. Analysis of the NOEs, coupling constants, and HN-DN exchange rates indicates the structure consists of an antiparallel beta-sheet from residues 25 to 36, with a type 1 turn at residues 30-31, and a helix from residues 13 to 21. The carboxyl-terminal residues form a short, and distorted, third strand of the sheet. The NMR data are consistent with disulfide bonds from residues 7 to 28, 13 to 33, and 17 to 35. The disulfide bridging presents the same profile as in other scorpion toxins, where a Cys-X-Cys sequence in a strand of sheet forms two disulfide bonds to a Cys-X-X-X-Cys sequence in a helix. Three-dimensional structures were generated using the torsion angle space program PEGASUS. The best ten structures had an average rmsd over all pairwise comparisons of 1.49 A. The average rmsd to a calculated average structure is 1.0 A. The resulting structures appear very similar to those of charybdotoxin, a related scorpion toxin.

  • determination of the three dimensional structure of Iberiotoxin in solution by 1h nuclear magnetic resonance spectroscopy
    Biochemistry, 1992
    Co-Authors: Bruce A Johnson, Elizabeth E Sugg
    Abstract:

    The solution structure of chemically synthesized Iberiotoxin, a scorpion toxin that blocks Ca 2+ -activated K + channels, has been determined using 2D 1 H NMR spectroscopy. Analysis of the NOEs, coupling constants, and HN-DN exchange rates indicates the structure consists of an antiparallel β-sheet from residues 25 to 36, with a type 1 turn at residues 30-31, and a helix from residues 13 to 21. The carboxyl-terminal residues form a short, and distorted, third strand of the sheet. The NMR data are consistent with disulfide bonds from residues 7 to 28, 13 to 33, and 17 to 35

William B. Campbell - One of the best experts on this subject based on the ideXlab platform.

  • Angiotensin II Regulates Adrenal Vascular Tone Through
    2016
    Co-Authors: Zona Glomerulosa, Phillip G Kopf, Kathryn M Gauthier, David X Zhang, John R Falck, William B. Campbell
    Abstract:

    Abstract—Elevated concentrations of aldosterone are associated with several cardiovascular diseases. Angiotensin II (Ang II) increases aldosterone secretion and adrenal blood flow. This concurrent increase in steroidogenesis and adrenal blood flow is not understood. We investigated the role of zona glomerulosa (ZG) cells in the regulation of vascular tone of bovine adrenal cortical arteries by Ang II. ZG cells enhanced endothelium-dependent relaxations to Ang II. The ZG cell–dependent relaxations to Ang II were unchanged by removing the endothelium-dependent response to Ang II. These ZG cell–mediated relaxations were ablated by cytochrome P450 inhibition, epoxyeicosatrienoic acid (EET) antagonism, and potassium channel blockade. Analysis of ZG cell EET production by liquid chromatography/mass spectrometry demonstrated an increase in EETs and dihydroxyeicosatrienoic acids with Ang II stimulation. These EETs and dihydroxyeicosatrienoic acids produced similar concentration-dependent relaxations of adrenal arteries, which were attenuated by EET antagonism. Whole-cell potassium currents of adrenal artery smooth muscle cells were increased by Ang II stimulation in the presence of ZG cells but decreased in the absence of ZG cells. This increase in potassium current was abolished by Iberiotoxin. Similarly, 14,15-EET induced concentration-dependent increases in potassium current, which was abolished by Iberiotoxin. ZG cell aldosterone release was not directly altered by EETs. These data suggest that Ang II stimulates ZG cells to release EETs and dihydroxyeicosatrienoic acids, resulting in potassium channel activation and relaxation of adrenal arteries. This provides a mechanism by which Ang II concurrently increase

  • angiotensin ii regulates adrenal vascular tone through zona glomerulosa cell derived eets and dhets
    Hypertension, 2011
    Co-Authors: Phillip G Kopf, Kathryn M Gauthier, David X Zhang, John R Falck, William B. Campbell
    Abstract:

    Elevated concentrations of aldosterone are associated with several cardiovascular diseases. Angiotensin II (Ang II) increases aldosterone secretion and adrenal blood flow. This concurrent increase in steroidogenesis and adrenal blood flow is not understood. We investigated the role of zona glomerulosa (ZG) cells in the regulation of vascular tone of bovine adrenal cortical arteries by Ang II. ZG cells enhanced endothelium-dependent relaxations to Ang II. The ZG cell–dependent relaxations to Ang II were unchanged by removing the endothelium-dependent response to Ang II. These ZG cell–mediated relaxations were ablated by cytochrome P450 inhibition, epoxyeicosatrienoic acid (EET) antagonism, and potassium channel blockade. Analysis of ZG cell EET production by liquid chromatography/mass spectrometry demonstrated an increase in EETs and dihydroxyeicosatrienoic acids with Ang II stimulation. These EETs and dihydroxyeicosatrienoic acids produced similar concentration-dependent relaxations of adrenal arteries, which were attenuated by EET antagonism. Whole-cell potassium currents of adrenal artery smooth muscle cells were increased by Ang II stimulation in the presence of ZG cells but decreased in the absence of ZG cells. This increase in potassium current was abolished by Iberiotoxin. Similarly, 14,15-EET induced concentration-dependent increases in potassium current, which was abolished by Iberiotoxin. ZG cell aldosterone release was not directly altered by EETs. These data suggest that Ang II stimulates ZG cells to release EETs and dihydroxyeicosatrienoic acids, resulting in potassium channel activation and relaxation of adrenal arteries. This provides a mechanism by which Ang II concurrently increases adrenal blood flow and steroidogenesis.

  • adrenic acid metabolites as endogenous endothelium derived and zona glomerulosa derived hyperpolarizing factors
    Hypertension, 2010
    Co-Authors: Phillip G Kopf, Xiu Yu Yi, Kasem Nithipatikom, Kathryn M Gauthier, David X Zhang, John R Falck, William B. Campbell
    Abstract:

    Adrenic acid (docosatetraenoic acid), an abundant fatty acid in the adrenal gland, is identical to arachidonic acid except for 2 additional carbons on the carboxyl end. Adrenic acid is metabolized by cyclooxygenases, cytochrome P450s, and lipoxygenases; however, little is known regarding the role of adrenic acid and its metabolites in vascular tone. Because of its abundance in the adrenal gland, we investigated the role of adrenic acid in vascular tone of bovine adrenal cortical arteries and its metabolism by bovine adrenal zona glomerulosa cells. In adrenal cortical arteries, adrenic acid caused concentration-dependent relaxations, which were inhibited by the epoxyeicosatrienoic acid antagonist 14,15-epoxyeicosa-5(Z)-enoic acid and the cytochrome P450 inhibitor SKF-525A. The large-conductance calcium-activated potassium channel blocker Iberiotoxin or removal of the endothelium abolished these relaxations. Reverse-phase high-pressure liquid chromatography and liquid chromatography/mass spectrometry isolated and identified numerous adrenic acid metabolites from zona glomerulosa cells, including dihomo-epoxyeicosatrienoic acids and dihomo-prostaglandins. In denuded adrenal cortical arteries, adrenic acid caused concentration-dependent relaxations in the presence of zona glomerulosa cells but not in their absence. These relaxations were inhibited by SKF-525A, 14,15-epoxyeicosa-5(Z)-enoic acid, and Iberiotoxin. Dihomo-16,17-epoxyeicosatrienoic acid caused concentration-dependent relaxations of adrenal cortical arteries, which were inhibited by 14,15-epoxyeicosa-5(Z)-enoic acid and high potassium. Our results suggest that adrenic acid relaxations of bovine adrenal cortical arteries are mediated by endothelial and zona glomerulosa cell cytochrome P450 metabolites. Thus, adrenic acid metabolites could function as endogenous endothelium-derived and zona glomerulosa-derived hyperpolarizing factors in the adrenal cortex and contribute to the regulation of adrenal blood flow.

Lih Kuo - One of the best experts on this subject based on the ideXlab platform.

  • resveratrol a component of red wine elicits dilation of isolated porcine retinal arterioles role of nitric oxide and potassium channels
    Investigative Ophthalmology & Visual Science, 2007
    Co-Authors: Lih Kuo, Taiji Nagaoka, Akitoshi Yoshida, Travis W Hein
    Abstract:

    Purpose Resveratrol, a polyphenolic phytoalexin found in grapes and red wine, has been shown to exert cardiovascular benefits, but its action in the retinal microcirculation remains unknown. In this study, the direct effect and the underlying mechanism of the vasomotor action of resveratrol were examined in retinal arterioles. Methods Porcine retinal arterioles were isolated, cannulated, and pressurized without flow for in vitro study. Resveratrol-induced diameter changes were recorded by videomicroscopic techniques. Results Retinal arterioles (65 +/- 3 microm) dilated dose dependently in response to resveratrol (1-50 microM). The removal of the endothelium reduced this dilation by 50%. Inhibition of nitric oxide (NO) synthase (by L-NAME; N(G)-nitro-L-arginine methyl ester) and blockade of soluble guanylyl cyclase (by ODQ; 1H-1,2,4-oxadiazolo[4,3-a]quinoxalin-1-one) produced similar inhibition as that produced by denudation. However, the resveratrol response was not affected by indomethacin (a cyclooxygenase inhibitor) and sulfaphenazole (an epoxygenase inhibitor). Intraluminal administration of an extracellular signal-regulated kinase (ERK) inhibitor (PD98059), but not an estrogen receptor blocker (ICI 182780), also reduced vasodilation by 50%. A nonselective K(+) channel blocker, tetraethylammonium (TEA), and a large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel inhibitor, Iberiotoxin, produced identical inhibition of resveratrol-induced dilation. However, the dilation was insensitive to the inhibitors of ATP-sensitive K(+) channels and voltage-gated K(+) channels. Coadministration of L-NAME and Iberiotoxin almost abolished the vasodilation induced by resveratrol. Conclusions Resveratrol elicits endothelium-dependent and -independent dilation of retinal arterioles. Endothelium-dependent dilation is mediated by the released NO, probably via NO synthase (NOS) activation by the ERK pathway and the subsequent activation of soluble guanylyl cyclase. The activation of BK(Ca) channels in smooth muscle contributes to the endothelium-independent dilation caused by resveratrol. A better understanding of the action of resveratrol on retinal vasculature may help shed light on its therapeutic potential for retinal vascular disease.

  • endothelial atp sensitive potassium channels mediate coronary microvascular dilation to hyperosmolarity
    American Journal of Physiology-heart and Circulatory Physiology, 1997
    Co-Authors: Hiroshi Ishizaka, Lih Kuo
    Abstract:

    Coronary arterial occlusion has been shown to increase osmolarity in the myocardial interstitium. Intracoronary injection of hyperosmolar solutions reduces coronary vascular resistance. However, the response of coronary microvessels to an abluminal increase in osmolarity is unclear, and the underlying mechanism for its vasomotor regulation has not been elucidated. In this regard, porcine coronary arterioles (81 +/- 2 microns) were isolated, cannulated, and pressurized for in vitro study. Hyperosmolarity (300-345 mosM) was produced by adding D-glucose or D-sucrose to the extravascular solution. After the arterioles developed a stable vascular tone, a graded vasodilation was observed when glucose or sucrose was incrementally administered. This hyperosmotic vasodilation was abolished after endothelial removal. Intraluminal administration of KCl (80 mM) or the ATP-sensitive potassium (KATP)-channel inhibitor glibenclamide (1 microM) to the intact vessels significantly attenuated the hyperosmotic vasodilation. Inhibition of inward rectifier potassium channels by a low concentration of BaCl2 (10 microM) did not affect vasodilation. However, a high concentration of BaCl2 (100 microM), which has been reported to inhibit KATP channels, attenuated the hyperosmotic vasodilation. Iberiotoxin (100 nM), a calcium-activated potassium (KCa)-channel inhibitor had no effect on hyperosmolarity-induced vasodilation. Inhibition of the synthesis of endothelial nitric oxide, prostaglandins, and arachidonic acid metabolites from cytochrome P-450 had no effect on hyperosmotic vasodilation. Furthermore, inhibition of vascular smooth muscle KATP channels and the large- and small-conductance KCa channels by extraluminal administration of glibenclamide, Iberiotoxin, and apamin, respectively, did not alter vasodilation in response to hyperosmolarity. These results indicate that dilation of coronary arterioles in response to hyperosmotic stimulation requires an intact endothelium. However, the response is independent of the release of nitric oxide, prostaglandins, or cytochrome P-450-related endothelium-derived hyperpolarizing factor and is not a result of activation of KATP and KCa channels in vascular smooth muscle. It is suggested that the opening of KATP channels in vascular endothelium and subsequent hyperpolarization of that cell type mediate coronary microvascular dilation in response to hyperosmolarity.

Mark Nelson - One of the best experts on this subject based on the ideXlab platform.

  • erectile dysfunction in mice lacking the large conductance calcium activated potassium bk channel
    The Journal of Physiology, 2005
    Co-Authors: Matthias Werner, Andrea L Meredith, Peter Zvara, Richard W Aldrich, Mark Nelson
    Abstract:

    Penile erection is dependent on the nitric oxide (NO)/cGMP-dependent protein kinase I (PKGI) pathway. One important target of PKGI in smooth muscle is the large-conductance, calcium-activated potassium (BK) channel, which upon activation hyperpolarizes the smooth muscle cell membrane, causing relaxation. Relaxation of arterial and corpus cavernosum smooth muscle (CCSM) is necessary to increase blood flow into the corpora cavernosa that leads to penile tumescence. We investigated the functional role of BK channels in the corpus cavernosum utilizing a knock-out mouse lacking the Slo gene (Slo−/−) responsible for the pore-forming subunit of the BK channel. Whole-cell currents were recorded from isolated CCSM cells of Slo+/+ and Slo−/− mice. Iberiotoxin-sensitive voltage- and [Ca2+]-activated K+ currents, the latter activated by local transient calcium releases (calcium sparks), were present in Slo+/+ CCSM cells, but absent in Slo−/− cells. CCSM strips from Slo−/− mice demonstrated a four-fold increase in phasic contractions, in the presence of phenylephrine. Nerve-evoked relaxations of precontracted strips were reduced by 50%, both in strips from Slo−/− mice and by blocking BK channels with Iberiotoxin in the Slo+/+ strips. Consistent with the in vitro results, in vivo intracavernous pressure exhibited pronounced oscillations in Slo−/− mice, but not in Slo+/+ mice. Furthermore, intracavernous pressure increases to nerve stimulation, in vivo, were reduced by 22% in Slo−/−mice. These results indicate that the BK channel has an important role in erectile function, and loss of the BK channel leads to erectile dysfunction.

  • ryanodine receptors regulate arterial diameter and wall ca2 in cerebral arteries of rat via ca2 dependent k channels
    The Journal of Physiology, 1998
    Co-Authors: Harm J Knot, Nicholas B Standen, Mark Nelson
    Abstract:

    1. The effects of inhibitors of ryanodine-sensitive calcium release (RyR) channels in the sarcoplasmic reticulum (SR) and Ca2+-dependent potassium (KCa) channels on the membrane potential, intracellular [Ca2+], and diameters of small pressurized (60 mmHg) cerebral arteries (100-200 micron) were studied using digital fluorescence video imaging of arterial diameter and wall [Ca2+], combined with microelectrode measurements of arterial membrane potential. 2. Ryanodine (10 microM), an inhibitor of RyR channels, depolarized by 9 mV, increased intracellular [Ca2+] by 46 nM and constricted pressurized (to 60 mmHg) arteries with myogenic tone by 44 micron (approximately 22 %). Iberiotoxin (100 nM), a blocker of KCa channels, under the same conditions, depolarized the arteries by 10 mV, increased arterial wall calcium by 51 nM, and constricted by 37 micron (approximately 19 %). The effects of ryanodine and Iberiotoxin were not additive and were blocked by inhibitors of voltage-dependent Ca2+ channels. 3. Caffeine (10 mM), an activator of RyR channels, transiently increased arterial wall [Ca2+] by 136 +/- 9 nM in control arteries and by 158 +/- 12 nM in the presence of Iberiotoxin. Caffeine was relatively ineffective in the presence of ryanodine, increasing [calcium] by 18 +/- 5 nM. 4. In the presence of blockers of voltage-dependent Ca2+ channels (nimodipine, diltiazem), ryanodine and inhibitors of the SR calcium ATPase (thapsigargin, cyclopiazonic acid) were without effect on arterial wall [Ca2+] and diameter. 5. These results suggest that local Ca2+ release originating from RyR channels (Ca2+ sparks) in the SR of arterial smooth muscle regulates myogenic tone in cerebral arteries solely through activation of KCa channels, which regulate membrane potential through tonic hyperpolarization, thus limiting Ca2+ entry through L-type voltage-dependent Ca2+ channels. KCa channels therefore act as a negative feedback control element regulating arterial diameter through a reduction in global intracellular free [Ca2+].

  • ca 2 activated k channels regulate action potential repolarization in urinary bladder smooth muscle
    American Journal of Physiology-cell Physiology, 1997
    Co-Authors: Thomas J Heppner, Adrian D Bonev, Mark Nelson
    Abstract:

    The goal of this study was to examine the role of large conductance Ca(2+)-activated K+ channels in the regulation of cell excitability in urinary bladder smooth muscle from the guinea pig. Ca(2+)-activated K+ channels were studied with single-channel recording techniques and found to be intracellular Ca2+ and voltage dependent and sensitive to external tetraethylammonium and blocked by nanomolar concentrations of Iberiotoxin (apparent dissociation constant of 4 nM). Spontaneous action potentials recorded from intact tissue strips depended on external Ca2+ and were inhibited by Ca2+ channel blockers. Iberiotoxin (100 nM) significantly altered the configuration of the action potential by increasing the duration and peak amplitude of the action potential and decreasing the rate of decay. Iberiotoxin also increased the action potential frequency from 0.11 to 0.29 Hz. This study suggests that Ca(2+)-activated K+ channels play a significant role in the repolarization of the action potential and in the maintenance of the resting membrane potential of the urinary bladder smooth muscle.