Figure 11.

Evidence for reduced SR Ca²⁺ content in probenecid-treated fibers. (A) Individual traces of Ca²⁺ release flux from control fibers (left, seven fibers from three mice) and from fibers treated with 2 mM probenecid (middle, five fibers from two mice). The right panel shows the corresponding mean (±SD, grey shading) time course of Ca²⁺ release. Data are from the same group of fibers as in Fig. 2. Traces in the two groups were selected on the basis of their similar value for initial peak Ca²⁺ release flux of ∼20 µM.ms^-1, irrespective of the activation voltage. Notice that, following the initial peak, the Ca²⁺ release flux decreases to zero in the probenecid-treated fibers whereas a slowly decaying phase persists in the control fibers. (B) Time course of the total released Ca²⁺ calculated from the above traces in A. Total released Ca²⁺ rapidly reaches a steady level in the probenecid-treated fibers, whereas it keeps rising in the control fibers.