Figure 4. The effects of sensitizing the release channels to cytosolic Ca²⁺ by low doses of caffeine on the ability of local releases to induce propagating Ca²⁺ waves under conditions of reduced SR Ca²⁺ load.

A, linescan images of fluorescence changes induced by focal applications of caffeine (10 mM) before (a) and 20 s after introducing 0.5 mM caffeine to the bath (b). The experimental protocol is illustrated by the scheme at the top. [Ca²⁺]_o was 1 mM. Calibration bars: horizontal, 18 μm; vertical, 0.66 s. B, linear fits to the position of the propagating Ca²⁺ wave for the section in Ab defined by the arrows; the value of the mean wave velocity (v) is indicated. C, time-dependent changes in fluorescence at the sites of caffeine application (marked in corresponding images in A by bars) with (black traces) and without (grey traces) conditioning by 0.5 mM caffeine.