Figure 2.

Membrane potential dependence of changes in [Ca²⁺]_i in fibers from 4-month-old WT and sAnk1 KO mice. (A) Line-scan images of changes in [Ca²⁺]_i elicited under whole-cell voltage-clamp by 100 ms long progressively increasing membrane depolarizations ranging between −60 mV and +30 mV, with 10 mV increments every 500 ms in WT and KO fibers. Each cell was held at −80 mV and perfused with 10 mM EGTA. The scale bar in the left panel corresponds to both line-scans. (B) Temporal profile of the changes in [Ca²⁺]_i calculated from the corresponding images in panel A by averaging 50 lines in the spatial domain normalized to average resting F₀(x). (C) Voltage dependence of the changes in [Ca²⁺]_i. Values obtained for individual fibers were first fitted by a Boltzmann function (Equation (1)) and then normalized to the obtained maximum for a given fiber, and finally averaged over the fibers. Continuous lines represent the best fit of the Boltzmann function to the average values with parameters of k = 8.95 and 6.17 mV, and V₅₀ = −21.60 and −20.91 mV, for WT (n = 10) and KO (n = 9), respectively. (D,E) Pooled data for Δ[Ca²⁺]_i (D) and the total amount of Ca²⁺ released (E) at +30 mV depolarization from four WT and five KO mice. To assess the peak change in [Ca²⁺]_i (D) and the amount of Ca²⁺ released (E), 100 ms and 1 s long single pulses were used, respectively. Numbers in columns show the number of fibers averaged. * denotes significant difference from WT at p < 0.05.