Figure 3. Block of double (Y506A-I510A and Y506A-F509A) and triple (Y506A-F509A-I510A) mutant channels by ivabradine.

A, top, sample currents recorded at −140 mV from the two double mutant channels Y506A-I510A and Y506A-F509A in control (a) and after steady-state block by ivabradine 30 µM (b); A, bottom, time course of currents at −140 mV during ivabradine perfusion. B: dose-response relations; Hill fitting (full lines) yielded IC₅₀, nH values of 2213.0 µM, 0.7, 42.5 µM, 0.8, and 1215.0 µM and 0.68 for Y506A-I510A, Y506A-F509A, and Y506A-F509A-I510A respectively. Hill fitting of WT and Y506A block from Fig. 2 also drawn for comparison (dotted lines). The two double-mutant curves are significantly different between themselves and from that of WT channels (P<0.05); the Y506A-I510A and the Y506A-F509A-I510A curves are not significantly different (P<0.05).