Figure 3. Mechanism of the CtVm-induced elevation in somatic [Ca²⁺]_i.

A, when the endoplasmic reticulum Ca²⁺ store was first depleted by bath application of the Ca²⁺-ATPase inhibitor thapsigargin (1 μM), subsequent application of CtVm produced only a modest, 35 nM elevation of somatic [Ca²⁺]_i. B, similarly, bath application of a different Ca²⁺-ATPase inhibitor, cyclopiazonic acid (10 μM), essentially eliminated the response to CtVm. C, the group data for the thapsigargin experiments demonstrate that application of CtVm following endoplasmic reticulum Ca²⁺ depletion produced a significantly lower response as compared with parallel controls performed in Ca²⁺-free ASW alone (P < 0.01, paired t test). In addition, prior application of cyclopiazonic acid results in an even further reduction of the CtVm-induced elevation of somatic [Ca²⁺]_i (P < 0.002, paired t test).