Figure 3. Effects of TK-inhibitor tyrphostin A23 and the inactive tyrphostins A1 and A63 on I_Ks.

A, comparison of the effects of 20 μm tyrphostin A23 (A23) and 200 μm tyrphostin A1 (A1) on the amplitude of I_Ks in a representative myocyte. B, dependence of inhibition of I_Ks on the concentrations of tyrphostins A1, A23 and A63. Myocytes were treated with single concentrations of the drugs for ∼8 min. The Hill equation fitting the tyrphostin A23 data has an IC₅₀ of 4.1 ± 0.6 μm, and a coefficient of 0.93 ± 0.1. Number of myocytes is shown in parentheses.