Figure 6. β-adrenergic receptor stimulation enhances peak and late I_Ca.L during the action potential in Calm1^N98S/+ ventricular myocytes.

A and B, L-type Ca²⁺ currents (lower panels) elicited by “typical” action potential waveforms (upper panels) that had been pre-recorded from isoproterenol (50 nM) - treated Calm1^+/+ and Calm1^N98S/+ ventricular myocytes. Action potential waveforms were delivered at 1 Hz steady-state frequency in the presence of isoproterenol (50 nM). Each data point in an I_Ca.L trace represents the mean ± SEM of 20 and 22 cells isolated from 4 Calm1^+/+ and 4 Calm1^N98S/+ hearts, respectively. C and D, The same action potential waveforms and I_Ca.L traces shown in A and B at expanded time scales. E and F, Dot plots of total I_Ca.L (∫I_Ca.L; E) normalized to cell capacitance and peak I_Ca.L density during the ventricular action potential in isoproterenol-treated cardiomyocytes. AP: action potential. Horizontal lines indicate mean ± SEM; 20 cells from 4 Calm1^+/+ mice and 22 cells from 4 Calm1^N98S/+ mice. P values by ANOVA followed by Bonferroni test for post hoc comparison.