Figure 1. Effect of cytosolic PCr on spontaneous Ca²⁺ release.

A, records of the Fura-2 fluorescence ratio from a saponin-permeabilized ventricular myocyte. In the presence of 10 mm PCr, transient increases in the fluorescence ratio occurred due to spontaneous SR Ca²⁺ release (top trace). Withdrawal of PCr resulted in a decrease in the amplitude and frequency of the spontaneous transients (middle trace). This effect was reversible on reintroduction of 10 mm PCr (bottom trace). B, spontaneous fluorescence transients in the presence and absence of PCr are shown superimposed and normalized on an expanded time scale. C, accumulated data from 9 myocytes showing the effects of PCr withdrawal on the mean time for the spontaneous transient to rise from 25 to 100 % of the maximum value (TP75) or to fall by 75 % of the peak level (DT75). Also shown is the effect of PCr withdrawal on the amplitude and frequency of spontaneous Ca²⁺ release. Each point represents the mean + s.e.m.