Figure 5. Higher SR Ca²⁺ release during EC coupling in TS cells increases the rate of inactivation of I_Ca.

A–B, representative I_Ca records normalized to peak from TS and WT myocytes dialyzed with an intracellular solution containing (A) or lacking (B) 10 mM of the Ca²⁺ chelator EGTA. Currents were evoked by a voltage step from −50 mV to 0 mV in the presence of 2 mM external Ca²⁺. Below, bar plots of the mean ± S.E.M. of the inactivation components of I_Ca: τ_fast (ms), τ_slow (ms), and current integral (fC/pF) in WT and TS myocytes. C, representative I_Ca and confocal line-scan images from WT (i) and TS (ii) cells. I_Ca and [Ca²⁺]_i transients were evoked by a 200 ms voltage step from −50 to 0 mV. Traces showing the time course of I_Ca and [Ca²⁺]_i in these cells are shown below and above the line-scan images, respectively. D, voltage dependence of the amplitude of the [Ca²⁺]_i transient on positive y-axis, current-voltage relationship of I_Ca on negative y-axis, for both WT (black) and TS (red) cells. E, voltage dependence of EC coupling (ECC) gain for WT (black) and TS (red).