Intracellular potassium activity in the rabbit proximal straight tubule

Abstract

Double-barreled liquid ion-exchanger microelectrodes were used to measure basolateral membrane potential (VBL) and intracellular K activity .**GRAPHIC**. in superficial proximal straight tubules (sPST) of the rabbit perfused in vitro. The mean .+-. SE (number of cells in parentheses) value of VBL was -37.8 .+-. 2.49 (20) mV and .**GRAPHIC**. was 48.6 .+-. 2.27 (20) mM. The calculated Nernst equilibrium potential (EK) across the basolateral membrane was -68 mV. Lowering bath K concentration to 0.1 mM reversibly decreased both VBL and .**GRAPHIC**. to -12.2 .+-. 1.21 (19) mV and 11.3 .+-. 1.29 (19) mM, respectively. Bath ouabain (10-5) resulted in similar changes. Intracellular K is actively accumulated in sPST perfused in vitro and that accumulation results primarily from Na-K-ATPase activity in the basolateral membrane. During recovery from low K bath, the temporal relationship between VBL and .**GRAPHIC**. and the effects of ouabain and high K bath on recovery are used to demonstrate directly electrogenic pumping. Lowering bath pH to 6.7 (HCO3- = 5 mM) and the presence of 0.5 mM BaCl2 in the bath resulted in a large and rapid depolarization of VBL with little or no change in .**GRAPHIC**. These results suggest that the response of VBL to both maneuvers is caused by a decrease in K permeability of the basolateral membrane.