Properties of Na +-dependent K + conductance in the apical membrane of frog taste cells

Abstract

Na +-dependent K + conductance observed in apical membrane of isolated bullfrog taste cells was analyzed using various modifications of the patch clamp method. When the apical receptive membrane of a taste cell was exposed to 0.5 M NaCl using a pipette perfusion method, an inward current appeared in the cell-attached patch membrane. The permeability ratio of Na + to K + ( P Na/ P K) calculated from the reversal potential was 0.3. When an outside-out patch from the receptive membrane was exposed to 0.25 M NaCl solution, two types of K + channel, whose conductance were 35.8 and 9.4 pS respectively, were activated. These channels were reversibly activated by increasing internal Na + concentration. In the whole cell configuration, the outward current evoked by a voltage ramp from −808561 to 80 mV was significantly suppressed by replacement of Na + by N-methyl- d-glucamine^ (NMDG +). The Na +-dependent outward current was blocked by 10 mM BaCl 2, with positive shift of the zero-current potential in the whole cell recordings, indicating that the outward current including Na +-dependent K + component contributes to maintenance of the resting potential. These results suggest that small conductance Na +-dependent K + channels, which are also permeable to Na +, are involved in salt signal transduction in frog taste cells.