Basolateral pH-sensitive K+ channels mediate membrane potential of proximal tubule cells in bullfrog kidney

The present study investigated basolateral K+ channels and their pH-sensitivity in isolated bullfrog proximal tubule cells by using the patch-clamp technique, and compared channel activity with the basolateral membrane potential (E-M) and intracellular pH (pH(i)) monitored by using double-barreled H+-selective microelectrodes in perfused bullfrog proximal tubules. In the patch-clamp experiments, K+ channels with inward slope conductance of about 50 pS were observed in the basolateral membrane of isolated proximal tubule cells in cell-attached patches. Raising pH of the bath with HCO3--free HEPES Ringer solutions from 7.7 (control) to 8.2 in the presence of an H+ ionophore, FCCP (2 mu M), enhanced channel activity to 126.4% of controls; lowering bath pH to 7.2 and to 6.7 reduced channel activity to 26.4 and to 1.7% of controls, Microelectrode experiments in bullfrog proximal tubules perfused with HCO3--free HERES Ringer solutions showed that E-M and pH(i) in control conditions of peritubular pH 7.7 without FCCP were -52.6mV and 7.45, Raising peritubular pH to 8.2 in the presence of FCCP (2 mu M) increased EM and pH(i) to -61.8 mV and 7.73; lowering it to 7.2 and to 6.7 decreased E-M and pH(i) to -28.6 mV and 7.25 and to -10.6 mV and 6.95, These results suggest that changes in E-M in response to cellular alkalinization or acidification made by HCO3--free HERES solutions are produced primarily by changes in activity of the pH-sensitive K+ channels.