Regulation of the basolateral potassium conductance of the Necturus proximal tubule

Two methods, the measurement of the response of the basolateral membrane potential (V_bl) of proximal tubule cells of Necturus to step changes in basolateral K⁺ concentration, and cellular cable analysis, were used to assess the changes in basolateral potassium conductance (G_K) caused by a variety of maneuvers. The effects of some of these maneuvers on intracellular K⁺ activity (a_Kⁱ) were also evaluated using double-barreled ion-selective electrodes. Perfusion with 0 mm K⁺ basolateral solution for 15 min followed by 45 min of 1 mm K⁺ solution resulted in a fall in basolateral potassium (apparent) transference number (t_K), V_bl and a_Kⁱ. Results of cable analysis showed that total basolateral resistance, R_b, rose. The electrophysiological effects of additional manipulations, known to inhibit net sodium reabsorption across the proximal tubular epithelium of Necturus, were also investigated. Ouabain caused a fall in t_K accompanied by large decreases in a_Kⁱ and V_bl. Lowering luminal sodium caused a fall in t_K and a small reduction in V_bl. Selective reduction of peritubular sodium, a maneuver that has been shown to block sodium transport from lumen to peritubular fluid, also resulted in a significant decrease in t_K. These results suggest that G_K varies directly with rate of transport of the sodium pump, irrespective of the mechanism of change in pump turnover.