Depolarization in the absence of external Ca2+ eliminates the fast, transient Ca
2+ and force signals. Intracellular Ca2+ (ratio 340/380, blue) and force (red) upon depolarization from 5.9 mM K+ to 124 mM K+ in the presence of 2.5 mM external Ca2+ (124 mM K+, A) or after re-addition of 3.5 mM Ca2+ to 0Ca (124 K+/0-3.5Ca, B). Pair-wise subtraction of 124 mM K+/0-3.5Ca from 124 mM K+ signals yielded the differential curves for Ca2+ (C) and force (D). Results show mean ± s.e.m, n = 4.