Figure 4.
Dependence of IKs blockade by 293B upon pulse duration. An SA node cell was depolarized every 10 s from a holding potential of −50 mV to a test potential of +50 mV for 400 ms before and during exposure to 293B at a given concentration (1, 10 or 100 μM). The cell was usually exposed to 293B for 2–3 min, which evoked a steady-state block. After washing 293B off for more than 3 min, the same cell was then depolarized every 20 s to +50 mV for 4000 ms and was again exposed to 293B for more than 2 min to attain a steady-state block. Percentage block was measured as the fractional decrease in the amplitude of IKs tail current elicited upon return to a holding potential of −50 mV in the presence of 293B. The columns and bars represent the mean and s.e.m., respectively (n=6 at each group). There was a statistically significant difference between the two groups at each concentration of 293B (Student's paired t-test).