title: Ca2+ channels in the apical membrane of the toad urinary bladder.
abstract: Previously (Van Driessche et al. 1987) we showed that small inward (mucosa towards serosa) oriented short-circuit currents (Isc) were recorded through the toad urinary bladder when the mucosal side was exposed to Ca2+ free solutions containing K+, Na+ (+ amiloride), Cs+ or Rb+ as main cation. This current component is inhibitable by micromolar concentrations of mucosal La3+ and divalent cations (Ca2+, Cd2+) and is considerably elevated by oxytocin (0.1 U/ml). The present study demonstrates that the addition of 50 nmol/l Ag+ to the mucosal medium during oxytocin treatment caused an additional large increase of the La3+-sensitive Isc component. The power density spectrum of the fluctuation in current contained a Lorentzian component which was enhanced by oxytocin treatment. The Lorentzian component disappeared as a consequence of the administration of mucosal Ag+. In experiments with Ca2+, Ba2+ or Mg2+ as principal mucosal cation, the La3+-sensitive Isc component was negligible under control conditions and during oxytocin treatment. Mucosal Ag+ (40 nmol/l) elicited a large inward oriented current which was blockable by the calcium channel blockers, La3+ and Cd2+. Also the organic calcium entry blockers, nicardipine and verapamil (10 mumol/l) depressed the inward current considerably. Noise analysis of the currents carried by divalent cations showed a La3+-sensitive noise component. Oxytocin-Ag+ activated currents could not be recorded in the absence of the divalent cations or small inorganic cations, e.g. with solutions which contained N-methyl D-glucamine (NMDG) as main mucosal cation.
mesh_terms: D000818:Animals; D001464:Barium / Q000378:metabolism; D002024:Bufo marinus; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002412:Cations; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability / Q000187:drug effects; D004553:Electric Conductivity; D007473:Ion Channels / Q000502:physiology*; D007811:Lanthanum / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism; D009092:Mucous Membrane / Q000187:drug effects / Q000502:physiology; D009529:Nicardipine / Q000494:pharmacology; D010121:Oxytocin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012834:Silver / Q000494:pharmacology; D001743:Urinary Bladder / Q000502:physiology*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002412:Cations; D007473:Ion Channels; D002104:Cadmium; D001464:Barium; D012834:Silver; D010121:Oxytocin; D007811:Lanthanum; D014700:Verapamil; D009529:Nicardipine; D008274:Magnesium; D011188:Potassium; D002118:Calcium