Figure 5. Spontaneous miniature DD voltage fluctuations and beating of SANC are inhibited when either LCRs are suppressed by ryanodine or I_NCX is acutely inhibited by a Na⁺ poor solution.

A. Time course of DD variance (dots) and of the relative LCRs occurrence (bars) observed at different times during the measurement period (24 SANC). Inset shows that the average amplitude of DD fluctuations, calculated for the 50-ms segment preceding AP upstroke, is suppressed by ryanodine (from²⁷). B. Superimposed APs of representative rabbit SANC before and after treatment with 3 μmol/L ryanodine (from¹³). C. Linescan image of Ca²⁺ release with superimposed AP records during rapid sprits with Na⁺ free solution. Red curve superimposed on the last AP preceding spritz of Na⁺ free solution is a copy of the residual membrane potential oscillation observed during Na⁺-free solution spritz. Note that this maneuver suppressed late DD (see inset) and blocked the subsequent AP firing. (from¹⁹). D. A rapid switch to low-Na⁺ solution (during the time indicated by the bar) caused immediate cessation of spontaneous action potentials in guinea-pig SANC. Action potentials speedily reappeared following rapid switch back to normal Na⁺ solution (with permission from²⁹).