Cell pH regulation in rabbit outer medullary collecting duct cells: mechanisms of HCO3(-)-independent processes

Abstract

To clarify mechanisms of intracellular pH (pHi) regulation in outer stripe of outer medullary collecting duct (OMCDOS), isolated perfused OMCDOS of the rabbit were loaded with 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF), and single cell pHi was monitored by an image processing system. Initial pHi recovery rates (dpHi/dt, pH unit/s x 10(3)) after intracellular acid load made by NH4Cl prepulse were determined. In the absence of exogenous CO2-HCO3-, dpHi/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 pHi recovery (dpHi/dt = 0.6 +/- 0.5), and pHi recovered when Na+ was added to the basolateral (dpHi/dt = 14.7 +/- 0.8) but not to the luminal (dpHi/dt = 0.9 +/- 0.5) solutions. This bath Na+ effect was amiloride inhibitable. In IC, pHi recovered (dpHi/dt = 6.4 +/- 0.3) in the absence of ambient Na+. This pHi 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 pHi 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 OMCDOS.