Evidence for separate cellular origins of sodium and acid-base transport in the turtle bladder.

Transmembrane electrical parameters of the epithelial cells in short-circuited turtle bladders were measured to determine whether those cells participating in Na reabsorption also participate in electrogenic transepithelial acidification and alkalinization. Amiloride-induced increases in intracellular potential (Vsca), apical fractional resistance (FRa), and concomitant decreases in short-circuit current (Isc) denote the participation of the impaled cells in Na reabsorption. In bladders from postabsorptive turtles, amiloride increased Vsca by -45 mV, increased FRa by 37%, and decreased Isc from 36 to -10 microA/cm2. In bladders from NaHCO3-loaded turtles, amiloride increased Vsca by -21 mV, FRa by 21%, and decreased Isc from 22 to 0 microA/cm2. Neither the subsequent inhibition of the negative acidification current in postabsorptive bladders, nor stimulation of positive alkalinization current in bladders from NaHCO3-loaded turtles was associated with any transmembrane electrical change that could be attributed to changes in those transport processes. It is concluded that the electrogenic luminal acidification and alkalinization processes of the turtle bladder are not produced by, or electrically coupled to, those cells that are involved in Na reabsorption.