Effects of membrane potential on IKACh evoked by Ado through A1R in guinea pig atrial myocytes.
a) Examples of IKACh traces elicited when sequentially perfusing the cells with increasing Ado concentrations and recorded at Vh of +30 mV (red traces) and -100 mV (black traces). The zero current level is indicated by the dashed line. b) C-R relationships for IKACh activated by Ado at Vh +30 mV (red circles) and -100 mV (black squares). The filled symbols represent the current amplitudes normalized to that activated by 100 μM Ado. The solid lines depict the best data fit to a Hill equation. The pEC50 values are reported in the text. The maximum asymptote (0.98 ± 0.01 at +30 mV and 1.00 ± 0.01 at -100 mV) was not significantly altered by voltage (P = 0.16; Wilcoxon signed rank test) neither was the Hill coefficient (1.03 ± 0.12 at +30 mV and 1.02 ± 0.09 at -100 mV) (P = 0.98; paired t test). n = 9 myocytes. For this and subsequent figures, the filled symbols represent the mean values, while the open symbols denote the individual raw data points.