Figure 1.

Comparison between [Ca²⁺]_i responses evoked by weak and strong depolarization. (A) [Ca²⁺]_i responses elicited by 30 mM K⁺ (left) and 50 mM K⁺ before (middle) and during (right) maintained exposure to 1 μM FCCP. Solid curve during the recovery after weak depolarization represents a single exponential (in nM): 35.5 + 242exp(−t/31.3 s). Cell sc0c45. (B) Plots of the total Ca²⁺ flux (J = −d[Ca²⁺]_i /dt) vs [Ca²⁺]_i for each recovery in A, showing the [Ca²⁺]_i dependence of Ca²⁺ removal rate. After small [Ca²⁺]_i elevations, recoveries are nearly exponential (linear in the J/[Ca²⁺]_i plot, dashed line), while recoveries after larger [Ca²⁺]_i elevations have two additional components: an outward flux at high [Ca²⁺]_i and an inward flux at lower [Ca²⁺]_i. In the presence of FCCP, the rate of Ca²⁺ removal is nearly proportional to [Ca²⁺]_i over the majority of the [Ca²⁺]_i range, much like the recovery after weak depolarization, but becomes limited at high [Ca²⁺]_i.