Ca²⁺ transients in response to trains of depolarizing steps in Dr-VSP–expressing fibers. (A) Control and test voltage-pulse protocols. (B) Rhod-2 F/F₀ traces recorded in response to the protocols shown in A in a Dr-VSP–positive fiber. (C) Mean values for the normalized ratio of peak F/F₀ during the test record to the corresponding peak F/F₀ during the control record, versus the pulse number in Dr-VSP–positive fibers (n = 7). Mean values for VSP-negative fibers are the same as in Fig. 4. Error bars represent ± SEM.