Figure 3.

Separation of the total Ca²⁺ flux during the recovery into mitochondrial and nonmitochondrial components. (A) [Ca²⁺]_i response elicited by exposure to 50 mM K⁺, illustrating the four phases of recovery (i–iv). Arrow indicates the [Ca²⁺]_i plateau. Cell sc0c73. (B) [Ca²⁺]_i dependence of the total Ca²⁺ flux (J_cont, thick trace) obtained by calculating −d[Ca²⁺]_i/dt during the recovery in A and plotting against [Ca²⁺]_i. The FCCP-resistant component of J_cont (J_FCCP-res, thin trace) was determined in the same cell during exposure to FCCP (1 μM). Average fluxes from 10 cells are shown at right (± SEM indicated by light traces). (C) J_mito, calculated by subtracting J_FCCP-res from J_cont at corresponding values of [Ca²⁺]_i for the single cell (left) and collected results (right). Arrows indicate the [Ca²⁺]_i plateau level. (D) Comparison between J_cont (thick trace) and its component fluxes J_mito and J_FCCP-res (thin traces) on an expanded scale, showing that, while J_cont is small during the plateau phase, it is the sum of much larger component fluxes of opposite sign that have similar magnitudes. Right panel shows collected results.