Figure 1. Experimental protocol.

A, voltage clamp protocol to evoke twitch contractions with various sized I_Ca in a cell whose SR was repeatedly loaded with the same conditioning regime. Pre-inactivation followed by depolarization, always to 0 mV, was used to vary I_Ca without changing unitary Ca²⁺ flux. B, immediately after the protocol shown in A, the same conditioning was repeated, followed by application of 10 mm caffeine, to measure the conditioned load. C, example showing substantially overlapping (grey background) I_Ca magnitudes attained ± ISO by adjusting pre-inactivation voltage (all traces from same cell).