Fig. 6

Effects of KB-R7943 on membrane potential and membrane currents at 37°C. A Upper a typical trace of membrane potential measured in the current-clamp mode. The myocyte was perfused with Ca-free Tyrode’s solution, and 20 μM KB-R7943 was added to the perfusate as shown above by a horizontal bar. At times indicated by asterisks (a, b and c), the myocyte was voltage-clamped to measure membrane currents. Lower traces in a, b and c show whole-cell currents recorded under voltage-clamp at asterisks marked a, b and c, respectively, in the upper panel. The holding potential was −66 mV (after correction of the junction potential, see text) and 200-ms hyperpolarizing pulses were applied in 10-mV increments as shown at the top of a. B Summary of membrane potential recorded in experiments of the type shown in A. Membrane potential was averaged over 30 s at the beginning of the current-clamp measurement (Before), just before the voltage-clamp run in the presence of KB-R7943 (KB-R7943) and at the steady level after washout of KB-R7943 (Washout). C Current–voltage relationships of whole-cell currents before (squares) and during (circles) application of KB-R7943. Current amplitudes at 61 ms after the onset of the hyperpolarizing pulses were plotted as a function of membrane potential. Note inwardly going rectification of the current. In B and C, each symbol represents mean ± SEM values from 7 cells