Figure 4.

Single channel current and SR Ca²⁺ release induced by depolarization and subsequent hyperpolarization. (A) Representative traces of single Ca²⁺ channel current recorded in the presence of 10 μM FPL, during depolarizing pulses (50 ms) to −30, 0, and +30 mV followed by hyperpolarizing steps to −120 mV. C, O, and T, mark the i_Ca when the channel was closed, open, and open during hyperpolarization (tail opening), respectively. Notice the multi-fold step increase in i_Ca upon hyperpolarization. (B) Representative line-scan images, spatially averaged OG-5N fluorescence signals and I_Ca simultaneously recorded in a myocyte. (C) Peak Ca²⁺ release fluxes elicited by a depolarizing pulse (to −30, 0, +30, or +60 mV, black bars) followed by a hyperpolarizing step (gray bars). (D) Cumulative Ca²⁺ release elicited by both depolarizing and hyperpolarizing pulses quantified by integrating f_r. Bar graphs C and D are the averaged data from five cells.