title: Calcium ionophore-induced changes in HCO3- secretion and Cl- absorption in turtle bladder: relation to action of 3-isobutyl-1-methylxanthine.
abstract: The calcium ionophore A23187 stimulates luminal alkalinization and inhibits Cl- absorption in short-circuited urinary bladders of postprandial or alkalotic turtles. The ionophore appears to mimic the action of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) by its similar effects on HCO3- secretion and Cl- absorption and by increasing cytosolic cAMP levels of isolated bladder epithelial cells. However, only A23187 (or ionomycin), but not IMBX or cAMP, elevated cytosolic Ca2+ of aequorin- or quin2-loaded cells. Since A23187, but not IBMX or cAMP inhibits luminal acidification, we postulate that cytosolic Ca2+ regulates the acidification process by a cAMP-independent mechanism and controls HCO3- secretion as well as Cl- absorption, at least in part, via cAMP-mediated pathways.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D000042:Absorption; D000818:Animals; D000838:Anions; D001639:Bicarbonates / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D013806:Theophylline / Q000031:analogs & derivatives*; D014426:Turtles / Q000378:metabolism*; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000838:Anions; D001639:Bicarbonates; D002712:Chlorides; D000001:Calcimycin; D013806:Theophylline; D000242:Cyclic AMP; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine