Figure 5. Comparative effects of CPA and ionomycin.

A, after two control responses to caffeine, 4 μm CPA was introduced into the perfusing solution. This resulted in a transient increase in the amplitude of the caffeine-induced Ca²⁺ transient followed by a marked decline over 4-6 min. The superimposed responses on an expanded time scale (right) show that the descending phase of the caffeine-induced Ca²⁺ transient is prolonged. B, after two control responses the Ca²⁺ permeability of the SR was increased by addition of 100 nM ionomycin. This resulted in a progressive decline in the amplitude of the Ca²⁺ transient, with little effect on the time course (right). Introduction of both CPA and ionomycin caused a slow transient release of Ca²⁺ from the SR.