Figure 3. The post-stimulation decay of mitochondrial [Ca²⁺] is accelerated by reducing bath [Ca²⁺] (A) and slowed by 3,4-diaminopyridine (3,4-DAP) (B).

A, responses to trains of 500 stimuli at 50 Hz measured in a motor terminal in a bath [Ca²⁺] of 1.8 and 0.4 mm. Similar changes were seen in another terminal (not shown) in which bath [Ca²⁺] was changed from 2.4 to 0.4 mm. B, responses to trains of 1000 stimuli at 50 Hz measured in another terminal before and 24 min after adding 100 μm 3,4-DAP. The constant amplitude of the peak increase in mitochondrial [Ca²⁺] in different bath [Ca²⁺] and after addition of 3,4-DAP is consistent with the hypothesized formation of an insoluble calcium-containing complex that limits the increase in matrix [Ca²⁺] (see Introduction). X-rhod-1 was used in both experiments.