Fig. 3. Sub-millimolar caffeine induces recruitment of central RyRs and enhances contraction during atrial EC-coupling. (A) The experimental protocol used to reversibly sensitise RyRs with 0.1 mM caffeine. (Ba-c) Traces showing the amplitude of electrically evoked Ca2+ responses at a peripheral site (black traces) and a central non-regenerative region (grey traces) before (a), during (b) and after washout (c) of 0.1 mM caffeine. The locations of the subcellular regions that were sampled are shown on the inset cell image. The dashed white line indicates the cell boundary, and the solid white line, the nucleus (N). (Ca-c) Traces depicting the twitch of the cell; a and c were obtained before caffeine application and after washout, respectively and b illustrates the enhancement of contraction observed during caffeine addition. A similar enhancement of contraction was observed in six out of six cells studied.