Effect of calcium ionophore A23187 on electrogenic acid-base transport in turtle bladder. Inhibition of acidification and stimulation of alkalinization.
Turtle bladders bathed on both surfaces with identical HCO3-/CO2-rich, Cl--free Na+ media and treated with ouabain and amiloride exhibit a transepithelial potential serosa electronegative to mucosa and a short-circuit current (Isc) which is a measure of the net luminal acidification rate. Addition of calcium ionophore A23187 (10 microM) to the mucosal side of the epithelium rapidly reverses the direction of the potential difference and Isc and decreases tissue resistance. The resulting positive Isc resembles that previously observed in response to isobutylmethylxanthine (IBMX) and cAMP analogs. Reversal of the Isc is enhanced in bladders from severely alkalotic turtles. In contrast, in severely acidotic turtles, ionophore A23187 decreases, but does not reverse, the Isc. The data suggest that, like IBMX and cAMP analogs, the Ca ionophore stimulates an electrogenic alkalinization mechanism, but, unlike the former agents, inhibits the concurrent acidification process as well.
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology*; D005016:Ethoxzolamide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D014426:Turtles; D001743:Urinary Bladder / Q000378:metabolism* / Q000502:physiology
D000900:Anti-Bacterial Agents; D001639:Bicarbonates; D000001:Calcimycin; D012964:Sodium; D005016:Ethoxzolamide