Fig. 3.
Carvedilol effect on voltage-gated Na+ current (INa). A and B: effect of 1 µM (A) and 10 µM (B) on INa: representative INa traces (a) and time course (b) of carvedilol effect on average peak INa corrected and normalized for rundown. A,b, insert: voltage-clamp protocol. Myocytes were held at membrane potential = −80 mV. A 2-step voltage-clamp protocol was applied to measure INa and L-type Ca2+ current (ICa) (Fig. 4) during the same experiment. INa was elicited with a 50-ms voltage step from −80 to −50 mV, immediately followed by a voltage step (350 ms) to 0 mV to elicit ICa. Upon completion of each step command, the command potential was returned to −80 mV for 1.4 s. A,c and B,c: summary data for uncorrected currents in control (Ctrl) and after 1- and 3-min carvedilol exposure. Means ± SE and individual cell data are shown (n = 8). *P < 0.02; **P < 0.003 (ANOVA). NS, not significant.