title: High [K+] alters the stimulus-hydrosmotic response coupling in toad bladder.
abstract: Substitution of K+ for Na+ in the Ringer solution bathing the inner surface of toad urinary bladders (Bufo marinus) had no effect on basal water permeability but significantly altered the stimulus-hydrosmotic response of this epithelium. In chloride-Ringer, high [K+] increased the hydrosmotic responses to submaximal stimulations induced by vasopressin or exogenous cAMP, while the responses to theophylline or serosal hypertonicity were decreased. In sulfate-Ringer, all these responses were enhanced but for that induced by serosal hypertonicity which was actually diminished. As a step towards determining if Ca2+ might mediate the K+-induced effects on water flow, experiments were conducted either in the presence of a Ca2+ "antagonist" (cobalt) or in nominally Ca2+-free Ringer. In both conditions the hydrosmotic effects of vasopressin and cAMP were markedly reduced. The results raise the possibility that a transient Ca2+ influx through voltage-sensitive, Co2+-blockade Ca2+ channels may play a role in the stimulus-hydrosmotic response of toad urinary bladder.
mesh_terms: D000818:Animals; D002024:Bufo marinus; D003035:Cobalt / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004594:Electrophysiology; D007552:Isotonic Solutions / Q000494:pharmacology; D008353:Mannitol / Q000494:pharmacology; D010539:Permeability; D011188:Potassium / Q000494:pharmacology*; D000077331:Ringer's Solution; D012867:Skin / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology; D001743:Urinary Bladder / Q000378:metabolism*; D014667:Vasopressins / Q000494:pharmacology; D014867:Water / Q000378:metabolism*
chemical_list: D007552:Isotonic Solutions; D014867:Water; D014667:Vasopressins; D003035:Cobalt; D008353:Mannitol; D012965:Sodium Chloride; D000077331:Ringer's Solution; D013806:Theophylline; D000242:Cyclic AMP; D011188:Potassium