Effects of vasoactive intestinal contractor on voltage-activated Ca2+ currents in feline parasympathetic neurons.
Intracellular current-clamp and single-electrode voltage-clamp techniques were used to study in vitro action potentials and the action of vasoactive intestinal contractor (VIC; 0.03-1 microM) on the high-voltage-activated Ca2+ currents (ICa) of neurons in feline colonic parasympathetic ganglia. In the current-clamp recording mode, action potential amplitude was depressed by cobalt (1 mM) and omega-conotoxin (300 nM) or in nominally Ca(2+)-free Krebs solutions. In the single-electrode voltage-clamp recording mode, the ICa was isolated by blocking the voltage-gated Na+ current with tetrodotoxin (1-3 microM) and by Krebs solutions containing a low Na+ concentration. The voltage-activated K+ currents were blocked by intracellular injection of cesium through a recording electrode filled with 2 M CsCl and external application of tetraethylammonium (30-50 mM) and barium (2 mM). The Ca(2+)-dependent Cl- current was blocked by replacement of Ca2+ (2 mM) with equimolar barium. Anomalous rectification was blocked by external application of 2 mM cesium. The ICa was evoked by depolarizing step commands more positive than -40 mV from holding potentials ranging between -80 and -60 mV. ICa was depressed by cobalt (1 mM), cadmium (100 microM), and omega-conotoxin (500 nM) but not by nifedipine (10 microM), nicardipine (10 microM), and verapamil (10 microM). BAY K 8644 (3-10 microM) also did not affect the ICa. VIC (0.1-1 microM), one of the endothelin (ET) isopeptides, caused an inward current followed by an outward current. The VIC-induced inward and outward currents were associated with an increase and decrease in membrane conductance, respectively. VIC also caused an initial depression followed by a long-lasting augmentation of the ICa. ET-1, ET-2, and ET-3 equally mimicked the action of VIC on both holding current and ICa. These data suggest that VIC activates a receptor-operated channel and modulates the omega-conotoxin-sensitive voltage-activated Ca2+ channels through ETB receptor subtypes of neurons in feline colonic parasympathetic ganglia.
Nishimura
T
T
Department of Physiology, Michigan State University, East Lansing 48824.
Krier
J
J
Akasu
T
T
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002415:Cats; D003106:Colon / Q000294:innervation*; D004594:Electrophysiology; D016232:Endothelins / Q000494:pharmacology; D005260:Female; D005726:Ganglia, Parasympathetic / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000294:innervation; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009529:Nicardipine / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D015220:Calcium Channels; D016232:Endothelins; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D013757:Tetraethylammonium Compounds; C059568:vasoactive intestinal constrictor; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D013779:Tetrodotoxin; D019789:Tetraethylammonium; D009529:Nicardipine; D009543:Nifedipine