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S H Chan - One of the best experts on this subject based on the ideXlab platform.
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Involvement of apamin-sensitive SK channels in spike frequency adaptation of neurons in nucleus tractus solitarii of the rat
Journal of Biomedical Science, 1999Co-Authors: J. C. Yen, Julie Y. H. Chan, S H ChanAbstract:We delineated the role of Ca^2+-activated K^+ channels in the phenomenon of spike frequency adaptation (SFA) exhibited by neurons in the caudal region of nucleus tractus solitarius (cNTS) using intracellular recording coupled with the Current-Clamp Technique in rat brain slices. Intracellular injection of a constant depolarizing Current evoked a train of action potentials whose discharge frequency declined rapidly to a lower steady-state level of irregular discharges. This manifested phenomenon of SFA was found to be related to extracellular Ca^2+. Low Ca^2+ (0.25 m M ) or Cd^2+ (0.5 m M ) in the perfusing medium resulted in a significant increase in the adaptation time constant (τ_adap) and an appreciable reduction in the percentage adaptation of spike frequency (F_adap). In addition, the evoked discharges were converted from an irregular to a regular pattern, accompanied by a profound increase in mean firing rate. Intriguingly, similar alterations in τ_adap, F_adap, discharge pattern and discharge rate were elicited by apamin (1 µ M ), a selective blocker for small-conductance Ca^2+-activated K^+ (SK) channels. On the other hand, charybdotoxin (0.1 µ M ), a selective blocker for large-conductance Ca^2+-activated K^+ channels, was ineffective. Our results suggest that SK channels of cNTS neurons may subserve the generation of both SFA and irregular discharge patterns displayed by action potentials evoked with a prolonged depolarizing Current.
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Passive biophysical membrane properties of nucleus reticularis gigantocellularis neurons in brain slices from the rat.
Neuroscience letters, 1993Co-Authors: J C Yen, S H ChanAbstract:This study employed intracellular recording coupled with the Current Clamp Technique to characterize the passive biophysical membrane properties of neurons in the nucleus reticularis gigantocellularis (NRGC) of brain slices from adult, male Sprague-Dawley rats. We found that NRGC neurons possessed highly depolarized transmembrane potentials (-22.9 +/- 0.6 mV, n = 189). The 29 NRGC neurons that received further evaluation showed that they could be separated into two clusters, with significantly different membrane input resistances (3.51 +/- 0.89 vs 77.50 +/- 8.82 M omega) and membrane time constants (0.56 +/- 0.05 vs 1.27 +/- 0.12 ms). These membrane properties, which resembled qualitatively those we observed previously in cats in vivo, will form the basis for further evaluation of the ionic mechanisms that may underlie the actions of pharmacologic agents on the NRGC neurons.
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Passive biophysical membrane properties of nucleus reticularis gigantocellularis neurons in brain slices from the rat
Neuroscience Letters, 1993Co-Authors: J C Yen, S H ChanAbstract:Abstract This study employed intracellular recording coupled with the Current Clamp Technique to characterize the passive biophysical membrane properties of neurons in the nucleus reticularis gigantocellularis (NRGC) of brain slices from adult, male Sprague-Dawley rats. We found that NRGC neurons possessed highly depolarized transmembrane potentials (−22.9 ± 0.6 mV, n = 189). The 29 NRGC neurons that received further evaluation showed that they could be separated into two clusters, with significantly different membrane input resistances (3.51 ± 0.89 vs 77.50 ± 8.82 M Ω ) and membrane time constants (0.56 ± 0.05 vs 1.27 ± 0.12 ms). These membrane properties, which resembled qualitatively those we observed previously in cats in vivo, will form the basis for further evaluation of the ionic mechanisms that may underlie the actions of pharmacologic agents on the NRGC neurons.
Tamotsu Takishima - One of the best experts on this subject based on the ideXlab platform.
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Diversity of early afterdepolarizations in guinea pig myocytes: Spatial characteristics of intracellular Ca^2+ concentration
Heart and Vessels, 1995Co-Authors: Masahito Miura, Nobumasa Ishide, Hirotaka Numaguchi, Tamotsu TakishimaAbstract:We classified early afterdepolarizations (EADs) into subgroups according to the spatial features of the intracellular Ca^2+ concentration ([Ca^2+]_i). Myocytes were enzymatically isolated from guinea pig ventricles. When fura-2 salt was applied through a whole cell patch pipette after the formation of a gigaohm seal, the membrane potential was measured using the Current, Clamp Technique. When myocytes were loaded with fura-2 AM, the membrane potential was recorded with a conventional microelectrode Technique. Spatio-temporal changes in fura-2 fluorescence and cell length were recorded simultaneously, using a digital TV system. EADs were induced after superfusion with potassium-free Tyrode solution. Irrespective of the fura-2 loading procedure, EADs could be classified into those with spatially synchronous fluorescence changes ( n = 26 from eight hearts) and those with heterogeneous changes ( n = 20 from three hearts). EADs with synchronous features took off from a higher membrane potential (≥−34mV) than EADs with heterogeneous features (≤−57 mV). These results suggest that EADs have at least two constituents.
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Diversity of early afterdepolarizations in guinea pig myocytes: spatial characteristics of intracellular Ca2+ concentration.
Heart and vessels, 1995Co-Authors: Masahito Miura, Nobumasa Ishide, Hirotaka Numaguchi, Tamotsu TakishimaAbstract:We classified early afterdepolarizations (EADs) into subgroups according to the spatial features of the intracellular Ca2+ concentration ([Ca2+]i). Myocytes were enzymatically isolated from guinea pig ventricles. When fura-2 salt was applied through a whole cell patch pipette after the formation of a gigaohm seal, the membrane potential was measured using the Current, Clamp Technique. When myocytes were loaded with fura-2 AM, the membrane potential was recorded with a conventional microelectrode Technique. Spatio-temporal changes in fura-2 fluorescence and cell length were recorded simultaneously, using a digital TV system. EADs were induced after superfusion with potassium-free Tyrode solution. Irrespective of the fura-2 loading procedure, EADs could be classified into those with spatially synchronous fluorescence changes (n = 26 from eight hearts) and those with heterogeneous changes (n = 20 from three hearts). EADs with synchronous features took off from a higher membrane potential (≥−34mV) than EADs with heterogeneous features (≤−57 mV). These results suggest that EADs have at least two constituents.
J C Yen - One of the best experts on this subject based on the ideXlab platform.
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Passive biophysical membrane properties of nucleus reticularis gigantocellularis neurons in brain slices from the rat.
Neuroscience letters, 1993Co-Authors: J C Yen, S H ChanAbstract:This study employed intracellular recording coupled with the Current Clamp Technique to characterize the passive biophysical membrane properties of neurons in the nucleus reticularis gigantocellularis (NRGC) of brain slices from adult, male Sprague-Dawley rats. We found that NRGC neurons possessed highly depolarized transmembrane potentials (-22.9 +/- 0.6 mV, n = 189). The 29 NRGC neurons that received further evaluation showed that they could be separated into two clusters, with significantly different membrane input resistances (3.51 +/- 0.89 vs 77.50 +/- 8.82 M omega) and membrane time constants (0.56 +/- 0.05 vs 1.27 +/- 0.12 ms). These membrane properties, which resembled qualitatively those we observed previously in cats in vivo, will form the basis for further evaluation of the ionic mechanisms that may underlie the actions of pharmacologic agents on the NRGC neurons.
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Passive biophysical membrane properties of nucleus reticularis gigantocellularis neurons in brain slices from the rat
Neuroscience Letters, 1993Co-Authors: J C Yen, S H ChanAbstract:Abstract This study employed intracellular recording coupled with the Current Clamp Technique to characterize the passive biophysical membrane properties of neurons in the nucleus reticularis gigantocellularis (NRGC) of brain slices from adult, male Sprague-Dawley rats. We found that NRGC neurons possessed highly depolarized transmembrane potentials (−22.9 ± 0.6 mV, n = 189). The 29 NRGC neurons that received further evaluation showed that they could be separated into two clusters, with significantly different membrane input resistances (3.51 ± 0.89 vs 77.50 ± 8.82 M Ω ) and membrane time constants (0.56 ± 0.05 vs 1.27 ± 0.12 ms). These membrane properties, which resembled qualitatively those we observed previously in cats in vivo, will form the basis for further evaluation of the ionic mechanisms that may underlie the actions of pharmacologic agents on the NRGC neurons.
Masahito Miura - One of the best experts on this subject based on the ideXlab platform.
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Diversity of early afterdepolarizations in guinea pig myocytes: Spatial characteristics of intracellular Ca^2+ concentration
Heart and Vessels, 1995Co-Authors: Masahito Miura, Nobumasa Ishide, Hirotaka Numaguchi, Tamotsu TakishimaAbstract:We classified early afterdepolarizations (EADs) into subgroups according to the spatial features of the intracellular Ca^2+ concentration ([Ca^2+]_i). Myocytes were enzymatically isolated from guinea pig ventricles. When fura-2 salt was applied through a whole cell patch pipette after the formation of a gigaohm seal, the membrane potential was measured using the Current, Clamp Technique. When myocytes were loaded with fura-2 AM, the membrane potential was recorded with a conventional microelectrode Technique. Spatio-temporal changes in fura-2 fluorescence and cell length were recorded simultaneously, using a digital TV system. EADs were induced after superfusion with potassium-free Tyrode solution. Irrespective of the fura-2 loading procedure, EADs could be classified into those with spatially synchronous fluorescence changes ( n = 26 from eight hearts) and those with heterogeneous changes ( n = 20 from three hearts). EADs with synchronous features took off from a higher membrane potential (≥−34mV) than EADs with heterogeneous features (≤−57 mV). These results suggest that EADs have at least two constituents.
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Diversity of early afterdepolarizations in guinea pig myocytes: spatial characteristics of intracellular Ca2+ concentration.
Heart and vessels, 1995Co-Authors: Masahito Miura, Nobumasa Ishide, Hirotaka Numaguchi, Tamotsu TakishimaAbstract:We classified early afterdepolarizations (EADs) into subgroups according to the spatial features of the intracellular Ca2+ concentration ([Ca2+]i). Myocytes were enzymatically isolated from guinea pig ventricles. When fura-2 salt was applied through a whole cell patch pipette after the formation of a gigaohm seal, the membrane potential was measured using the Current, Clamp Technique. When myocytes were loaded with fura-2 AM, the membrane potential was recorded with a conventional microelectrode Technique. Spatio-temporal changes in fura-2 fluorescence and cell length were recorded simultaneously, using a digital TV system. EADs were induced after superfusion with potassium-free Tyrode solution. Irrespective of the fura-2 loading procedure, EADs could be classified into those with spatially synchronous fluorescence changes (n = 26 from eight hearts) and those with heterogeneous changes (n = 20 from three hearts). EADs with synchronous features took off from a higher membrane potential (≥−34mV) than EADs with heterogeneous features (≤−57 mV). These results suggest that EADs have at least two constituents.
Richard Martin - One of the best experts on this subject based on the ideXlab platform.
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The time-course of the response to the FMRFamide-related peptide PF4 in Ascaris suum muscle cells indicates direct gating of a chloride ion-channel.
Parasitology, 2002Co-Authors: J. Purcell, Alan P. Robertson, D. P. Thompson, Richard MartinAbstract:We investigated the effects of PF4 on Ascaris suum somatic muscle cells using a 2 electrode Current-Clamp Technique. PF4 is a FaRP (FMRFamide-related peptide), originally isolated from the free-living nematode Panagrellus redivivus . PF4 caused hyperpolarization and an increase in chloride ion conductance when it was applied to the muscle cells of the Ascaris body wall. The delay between the application of the peptide and the appearance of the response was measured and compared with that of gamma-amino butyric acid (GABA), a compound that directly gates ion channels, and with PF1, a FaRP that acts via an intracellular signal transduction mechanism. The PF4 and GABA delay times were not significantly different; they were 1·51±0·11 sec and 1·22±0·10 sec respectively. The delay following application of PF1, 3·75±0·51 sec, was significantly longer. The rapid response to PF4 is consistent with direct gating of a chloride ion channel, which has not been described elsewhere in the literature.
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Anthelmintic actions of the cyclic depsipeptide PF1022A and its electrophysiological effects on muscle cells of Ascaris suum
Pesticide Science, 1996Co-Authors: Richard Martin, Achim Harder, Michael Londershausen, Peter JeschkeAbstract:The cyclic depsipeptide PF1022A, given orally to mice, showed very good anthelmintic activity against Heligmosomoides polygyrus and Heterakis spumosa at 50 mg kg -1 . In vitro, PF1022A was very active against Trichinella spiralis and had good activity against Nippostrongylus brasiliensis at 1 μg ml -1 . An 18-membered enniatin analogue, JES 1798, showed good activity only against N. brasiliensis at 10 μg ml -1 . The optical antipode of PF1022A had poor activity even at 100 μg ml -1 . The effects of PF1022A on the membrane potential and input conductance of somatic muscle of Ascaris suum were examined using a two-microelectrode Current-Clamp Technique. PF1022A did not antagonize the effects of the selective nicotinic agonist levamisole. PF1022A and an analogue, JES 1798, but not the PF1022A antipode, produced a small time-dependent increase in input conductance associated with no potential change. The increase in input conductance did not occur in the Cl - -free bathing solution, suggesting that the increase in input conductance was mediated by Cl - ions. The addition of high concentrations of Ca 2+ to the preparation after the addition of PF1022A did not lead to production of Ca 2+ -activated Cl - channels, suggesting that its mode of action was not that of a Ca 2+ ionophore. The mechanism by which the cyclic depsipeptide might increase the Cl - conductance is discussed.
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Novel arylaminopyridazine-GABA receptor antagonists examined electrophysiologically in Ascaris suum
European Journal of Pharmacology, 1995Co-Authors: Richard Martin, Jean-marie Sitamze, Anne Duittoz, Camille WermuthAbstract:The structure-activity relationships of 35 novel derivatives of 2-(carboxypropyl)-3-amino-4-methyl-6-phenyl pyridazine (SR 95103) were examined as gamma-aminobutyric acid (GABA) antagonists in the flap preparation of the parasitic nematode, Ascaris suum, using a two-microelectrode Current-Clamp Technique. All but one of the potent antagonists displaced GABA dose-response curves to the right without reduction in the maximum response. The dissociation constants of the more potent competitive antagonists were described using a model which assumed that two molecules of GABA were required to open the ion channel but that only one molecule of antagonist acted on each ion channel. By exploring the structure-activity relationship, the potency of the antagonist was increased from a KB of 64 microM for SR 95103 to a KB of 4.7 microM for NCS 281-93 (2-(3-carboxypropyl)-3-amino-4-phenylpropyl-6-phenyl pyridazine).
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Antagonist properties of arylaminopyridazine GABA derivatives at the Ascaris muscle GABA receptor
The Journal of Experimental Biology, 1991Co-Authors: A. H. Duittoz, Richard MartinAbstract:Summary 1. In a previous study, it was shown that the potency order for two arylaminopyridazine derivatives, SR95531 and SR95103, was different in Ascaris suum when compared to vertebrate preparations. SR95531, the most potent analogue at the vertebrate GABAA receptor, was found to be very weak at antagonizing GABA responses in Ascaris, but SR95103, approximately 20 times less potent than SR95531 in vertebrate preparations, was more potent than SR95531 in Ascaris. These results suggested the existence of different accessory binding sites at the Ascaris GABA receptor. 2. To test this hypothesis, the effects of a series of arylaminopyridazine derivatives of GABA on the GABA response in Ascaris suum muscle were investigated using a two-microelectrode Current-Clamp Technique. 3. The results showed that SR42627, a potent antagonist at the GABAA receptor, was one of the weakest analogues in Ascaris muscle. In contrast, SR95132, virtually inactive in vertebrate preparations, was equipotent to SR95103, the most potent analogue of the series in Ascaris muscle. 4. The three most potent analogues in Ascaris, SR95103, SR95132 and SR42666, displace GABA dose-response curves to the right without decreasing the maximal response. The modified Schild plots for these compounds are consistent with a competitive mechanism involving two molecules of GABA and only one molecule of antagonist interacting with the receptor. The estimated dissociation constants for SR95103, SR95132 and SR42666 are, respectively, 64, 65 and 105/zmoir 1 . 5. Structure-activity relationships for this series of compounds were examined in Ascaris and compared to those in vertebrates. Substitution on the pyridazine ring in the 4-position, while detrimental for the antagonist potency at the vertebrate GABAA receptor, appears to be a prerequisite for antagonistic activity on the Ascaris muscle GABA receptor. These results are interpreted in terms of the accessory binding site theory of Ariens, and suggest the existence of different accessory binding sites on the Ascaris GABA receptor.
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Antagonist properties of arylaminopyridazine GABA derivatives at the Ascaris muscle GABA receptor.
Journal of Experimental Biology, 1991Co-Authors: Anne Duittoz, Richard MartinAbstract:1. In a previous study, it was shown that the potency order for two arylamino-pyridazine derivatives, SR95531 and SR95103, was different in Ascaris suum when compared to vertebrate preparations. SR95531, the most potent analogue at the vertebrate GABAA receptor, was found to be very weak at antagonizing GABA responses in Ascaris, but SR95103, approximately 20 times less potent than SR95531 in vertebrate preparations, was more potent than SR95531 in Ascaris. These results suggested the existence of different accessory binding sites at the Ascaris GABA receptor. 2. To test this hypothesis, the effects of a series of arylaminopyridazine derivatives of GABA on the GABA response in Ascaris suum muscle were investigated using a two-microelectrode Current-Clamp Technique. 3. The results showed that SR42627, a potent antagonist at the GABAA receptor, was one of the weakest analogues in Ascaris muscle. In contrast, SR95132, virtually inactive in vertebrate preparations, was equipotent to SR95103, the most potent analogue of the series in Ascaris muscle. 4. The three most potent analogues in Ascaris, SR95103, SR95132 and SR42666, displace GABA dose-response curves to the right without decreasing the maximal response. The modified Schild plots for these compounds are consistent with a competitive mechanism involving two molecules of GABA and only one molecule of antagonist interacting with the receptor. The estimated dissociation constants for SR95103, SR95132 and SR42666 are, respectively, 64, 65 and 105 mumol l-1. 5. Structure-activity relationships for this series of compounds were examined in Ascaris and compared to those in vertebrates. Substitution on the pyridazine ring in the 4-position, while detrimental for the antagonist potency at the vertebrate GABAA receptor, appears to be a prerequisite for antagonistic activity on the Ascaris muscle GABA receptor. These results are interpreted in terms of the accessory binding site theory of Ariëns, and suggest the existence of different accessory binding sites on the Ascaris GABA receptor.
