Oscillation of membrane potential in L cells: III K + current-voltage curves.

Cultured L cells were found previously to have an oscillating membrane potential. Current-voltage (I--V) curves were measured during these oscillations. Two I--V curves were recorded, one at the maximum and one at the minimum of oscillations. Each curve is nonlinear, and when they are subtracted from one another, the result gives the I--V curve for the K+ current producing oscillations. This Ik--V curve is zero for -85 to -90 mV and saturates for positive and high negative membrane potentials. When the external K+ is increased the I--V curve is shifted and its zero current potential is reduced. The K+ zero current potential follows a Nernst relation when plotted against the external K+ concentration. The Ik--V curves all have a similar shape at different K+ concentrations, showing a saturation on each side of the zero current potential. The results can be explained satisfactorily in term of a carrier model for K+ ions.