BASOLATERAL PH-SENSITIVE K-POTENTIAL OF PROXIMAL TUBULE CELLS IN BULLFROG KIDNEY( CHANNELS MEDIATE MEMBRANE)

The present study investigated basolateral K+ channels and their pH-se nsitivity in isolated bullfrog proximal tubule cells by using the patc h-clamp technique, and compared channel activity with the basolateral membrane potential (E-M) and intracellular pH (pH(i)) monitored by usi ng double-barreled H+-selective microelectrodes in perfused bullfrog p roximal tubules. In the patch-clamp experiments, K+ channels with inwa rd slope conductance of about 50 pS were observed in the basolateral m embrane of isolated proximal tubule cells in cell-attached patches. Ra ising 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), enh anced 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, M icroelectrode experiments in bullfrog proximal tubules perfused with H CO3--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, R aising peritubular pH to 8.2 in the presence of FCCP (2 mu M) increase d EM and pH(i) to -61.8 mV and 7.73; lowering it to 7.2 and to 6.7 dec reased E-M and pH(i) to -28.6 mV and 7.25 and to -10.6 mV and 6.95, Th ese results suggest that changes in E-M in response to cellular alkali nization or acidification made by HCO3--free HERES solutions are produ ced primarily by changes in activity of the pH-sensitive K+ channels.