Figure 1. Time course of Ca²⁺ release induced by various concentrations of DP4.

(A) Time course of Ca²⁺ flux (100 units of the CTC fluorescence change correspond to a 0.15 mM change in luminal Ca²⁺). Initial phase corresponds to active uptake of Ca²⁺ following addition of MgATP (at t=10 s). Fluorescence intensity subsequently decreased owing to passive Ca²⁺ leak into the BAPTA-buffered extra-vesicular solution (control trace). Ca²⁺ efflux is accelerated when RyR agonists are added (50 μM DP4 was added at t=90 s). The Ca²⁺ gradient is rapidly ablated by the addition of 1 μM ionomycin. (B) Time courses of Ca²⁺ released from SR vesicles at various DP4 concentrations. External Ca²⁺ was held at 0.1 μM. Following subtraction of control data, traces were fitted to equations of the form y=A·e^−kt+y_o, where A is the maximum amount of Ca²⁺ release, k is the rate constant of Ca²⁺ release and t is time. (C) Plot of A·k (initial rate of release) against DP4 concentration.