Figure 4. Higher SR Ca²⁺ release during EC coupling in Endo than in Epi cells.

A, representative I_Ca and confocal line-scan images from Epi and Endo cells. I_Ca and [Ca²⁺]_i transients were evoked by a 200 ms voltage step from −40 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. B, current–voltage relationships of I_Ca in Epi and Endo cells. C, voltage dependence of the amplitude of the [Ca²⁺]_i transient in Epi and Endo cells. D, voltage dependence of EC coupling (ECC) gain.