Changes in voltage-activated SR Ca ²⁺ release flux during probenecid application. Data are from the same experiments as in Fig. 6. (A) Control experiment: rhod-2 Ca²⁺ transients (top, _initialF₀ unit) and corresponding SR Ca²⁺ release flux (bottom, µM.ms⁻¹) recorded in response to the voltage pulses shown at the top in a muscle fiber challenged by the test-control protocol (DMSO application) and after wash. (B) Test experiment, same measurements as in A from a muscle fiber challenged with probenecid and after wash.