Electrical Evidence from Perfused and Intact Cells for Voltage-dependent K+ Channels in the Plasmalemma of Chara australis

The K+ conductance in Chara australis was studied using current-voltage relations (I- V curves) of intact cells and perfused plasmalemmas in conditions which minimized H+ conductance. The rapid I-V curves of perfused cells were dominated by K+ conductance, intersecting at the calculated K' equilibrium potential. The steady state I-V curves were non-linear; the point of greatest change in slope conductance has been called the 'switch potential'. At voltages more positive than the switch potential, K+ conductance increased with potential. At more negative voltages, K+ conductance was constant and low. In high external K+ concentrations the steady state I-V curves developed negative slope conductance near the switch potential. The switch potential behaved as a function of the KC equilibrium potential. During prolonged voltage pulses in perfused cells, the clamp current changed exponentially with time. The values o f t , were affected by the size of the voltage pulse and the external KT concentration. The results can be explained by time- and voltage-dependent K+ channels. It is suggested that the voltage sensor, which supposedly regulates the opening and closing of the Kt channels, measures a function of the membrane potential and the K+ equilibrium potential.