Reversibility of the effect of VSP activation on trains of Ca²⁺ transients. (A) Pulse protocols that were successively applied. (B) F/F₀ rhod-2 traces elicited in a Ci-VSP–expressing fiber challenged by the protocols shown in A. (C) Mean values for the peak F/F₀ rhod-2 signals during the test 1, control 2, and test 2 records (n = 12 Ci-VSP–expressing fibers); in each fiber, successive peak F/F₀ values were divided by the corresponding values for the same pulse number during the control 1 record. Error bars represent ± SEM.