CELL PH REGULATION IN RABBIT OUTER MEDULLARY COLLECTING DUCT CELLS - MECHANISMS OF HCO3(-)-INDEPENDENT PROCESSES

To clarify mechanisms of intracellular pH (pH(i)) regulation in outer stripe of outer medullary collecting duct (OMCD(OS)), isolated perfused OMCD(OS) of the rabbit were loaded with 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF), and single cell pH(i) was monitored by an image processing system. Initial pH(i) recovery rates (dpH(i)/dt, pH unit/s x 10(3)) after intracellular acid load made by NH4Cl prepulse were determined. In the absence of exogenous CO2-HCO3-, dpH(i)/dt was 12.3 +/- 0.9 (means +/- SE) in principal cells (PC), and 11.5 +/- 1.0 in intercalated cells (IC). In PC, total ambient Na+ removal halted pH(i) recovery (dpH(i)/dt = 0.6 +/- 0.5), and pH(i) recovered when Na+ was added to the basolateral (dpH(i)/dt = 14.7 +/- 0.8) but not to the luminal (dpH(i)/dt = 0.9 +/- 0.5) solutions. This bath Na+ effect was amiloride inhibitable. In IC, pH(i) recovered (dpH(i)/dt = 6.4 +/- 0.3) in the absence of ambient Na+. This pH(i) recovery was significantly reduced by luminal 0.5 mM N-ethylmaleimide (NEM) or 0.5 mM N,N'-dicyclohexylcarbodiimide (DCCD). Basolateral NEM or DCCD had no significant effect. Basolateral addition of Na+ significantly accelerated the pH(i) recovery. These data suggest the presence of basolateral Na+-H+ exchange in both PC and IC, and luminal NEM- and DCCD-sensitive H+ pump in IC of rabbit OMCD(OS).