Voltage-activated Ca²⁺ release in VSP-expressing fibers. (A) Line-scan images of depolarization-induced Ca²⁺ release in a VSP-negative fiber (left) and in a Ci-VSP–expressing fiber (right); fibers were depolarized from −80 to 10 mV (traces on top). (B) Ca²⁺ transients (rhod-2 F/F₀, thick traces) and corresponding rate of Ca²⁺ release (thin red traces) in response to pulses from −80 mV to the indicated values. (C) Peak Ca²⁺ release versus voltage in VSP-negative fibers (n = 9) and in Ci-VSP–expressing fibers (n = 6). Error bars represent ± SEM. (D) Average Ca²⁺ release in response to a pulse from −80 to 10 mV in VSP-negative fibers (line) and in Ci-VSP–expressing fibers (blue squares).