Figure 1.
Effect of channel phosphorylation on the TTX-induced blockade. (a,c) Superimposed representative ICa records obtained in the presence of cumulatively increasing concentrations of TTX. Finally, TTX was washed out to demonstrate reversibility. Experiments were performed either in Tyrode solution (a) or in the presence of 3 μM forskolin (c). (b,d) Average results obtained with TTX in four untreated and five forskolin-treated myocytes (panels b and d, respectively). In both cases, peak ICa was normalized to the value measured prior to the first application of TTX. Columns and bars are the means ± SEM values; asterisks denote significant changes from the pre-TTX controls (Tyrode or forskolin, respectively). (e) Cumulative dose-response curves demonstrating the inhibitory effects of TTX in Tyrode solution (open symbols, dashed line) and in the presence of forskolin (filled symbols, solid line). IC50 values and Hill coefficients were determined by fitting data to the Hill equation.