Figure 3. Ca²⁺-independent currents in Xenopus RPE cells.

Holding potential was −20 mV. Cells were depolarized to +100 mV for 500 ms prior to hyperpolarizing to various potentials as shown in the voltage clamp protocol in A. A, current traces showing an instantaneous time-independent inward current followed by a slow time-dependent activation of an inward current upon hyperpolarization. Deactivating tail currents are observed upon depolarization to +50 mV. B, current-voltage relationships. ○, instantaneous current at onset of voltage pulse. This current was defined as I_bkg. ▵, total current at the end of the 1.5 s hyperpolarizing pulse. ▪, the time-dependent current obtained by subtracting the instantaneous current from the total current. This time-dependent current was defined as I_Cl,ir. C, activation curve for I_Cl,ir. The conductance (G) for I_Cl,ir was determined by measuring the instantaneous amplitude of the tail currents upon repolarizing to +50 mV as in A and dividing by the driving force (50 mV). G for each tail current was plotted vs. the voltage of the preceding hyperpolarizing pulse. (n = 5; ±s.e.m.).