Figure 3.

Inactivation of current through I_K,in is evoked by [Ca²⁺]_i elevation. Data are from one guard cell bathed in 5 mm Ca²⁺-Mes, pH 6.1, with 10 mm KCl. A, Clamp current recorded using standard two-pulse protocols of eight cycles with the addition of a third, 0.5-s intervening step at the end of each cycle to −250 mV (a) or to −30 mV (b). Clamp cycles: 0.5-s conditioning step, −100 mV; 2-s test steps (8) from +20 to −200 mV. B, Voltage (V, top trace) and [Ca²⁺]_i (bottom trace) records with intervening voltage steps numbered according to the cycle (1–8, cross-referenced to currents in A). The mean [Ca²⁺]_i during the final three cycles in each protocol is indicated by the solid lines overlaid on the [Ca²⁺]_i record. C, Steady-state current-voltage characteristic determined from the currents recorded at the end of the test voltage steps in protocols a and b. The curves have not been corrected for the background (“instantaneous”) current.