Acid-base metabolism, intracellular pH and water transport by the toad bladder

A decrease in extracellular pH is well known to inhibit vasopressin stimulated water flow in the toad bladder. It remains unclear whether this inhibition is the result of the effect of extracellular pH per se or the consequence of altered intracellular pH. In the present study we evaluated the effect of several maneuvers capable of altering intracellular pH on vasopressin or cyclic AMP stimulated water flow in the toad bladder in the absence of alterations of extracellular pH. In the presence of a normal extracellular pH, bladders subjected to a high partial pressure of CO2 or bladders from acidotic toads had a significant decrease in vasopressin or cyclic AMP stimulated water flow as compared to controls. We also examined the effect of maneuvers capable of increasing intracellular pH on vasopressin and cyclic AMP stimulated water flow. Intracellular alkalosis was induced by exposing the bladders in vitro to NH4Cl at pH 8 or to acetazolamide. Both maneuvers resulted in a significant decrease in vasopressin, but not in cyclic AMP stimulated water flow. Bladders removed from alkalotic toads, incubated in a normal extracellular pH also showed a decrease in AVP stimulated water flow. Intracellular muscle pH assessed with phosphorus nuclear magnetic resonance, was not different among bladders from control, acidotic and alkalotic toads. It is concluded that alterations of intracellular pH, in the absence of alterations of extracellular pH, are important in regulation of water transport in the toad bladder in response to vasopressin or cyclic AMP. In addition, metabolic acidosis or alkalosis alters AVP or cyclic AMP stimulated water flow by a mechanism independent of the intracellular pH.