Figure 2. Effects of Ca²⁺, InsP₃ and heparin on [Ca²⁺]_L.

A, following permeabilization in Ca²⁺-free ICM, addition of Ca²⁺ to ICM-1 mM EGTA (1 mM EGTA, 600 μM CaCl₂, [Ca²⁺]_free, 250 nM) caused rises in the mag-fura-2 ratio indicative of Ca²⁺ uptake into Ca²⁺-storing organelles. The subsequent incremental addition of InsP₃ resulted in graded declines of [Ca²⁺]_L. B, inhibition of InsP₃-induced Ca²⁺ release by heparin (1 mg ml⁻¹). Additions were made as indicated. The traces shown in A and B are representative of 6 and 3 independent experiments, respectively.