Chloride transport in the diluting segment of the K+ adapted frog kidney: effect of amiloride and acidosis.

The hypothesis was tested whether amiloride and/or an acute acid load influence Cl- transport in the diluting segment of the isolated-perfused kidney of the K+ adapted frog (rana pipiens). Transepithelial resistance (luminal cable analysis) and Cl- net flux (Cl- sensitive microelectrodes) were evaluated at various concentrations of amiloride, at high pCO2 or low HCO-3 in the kidney perfusate. Amiloride or an acute acid load increase transepithelial resistance. The resistance-change at given concentrations of amiloride is markedly enhanced under static head conditions, i.e. at low luminal NaCl concentrations. Amiloride or acidosis (high pCO2) reduce Cl- net reabsorption; combination of both potentiates this inhibitory effect. We conclude: an acute acid load acidifies the cell cytosol. This effect is aggravated dramatically after amiloride-induced inhibition of the luminal Na+/H+ exchanger. The luminal pH-sensitive K+ conductance decreases. This results in a depolarization of the cell membranes. Consequently, the peritubular electrochemical driving force for the exit step of Cl- (from cell to blood) dissipates. Therefore, Cl- net reabsorption is blunted.