Fig. 1

[Ca²⁺]_i increases following the reintroduction of Ca²⁺ during IM stimulation. a IM (1 μM). The addition of 1 μM IM in the Ca²⁺-free solution increased [Ca²⁺]_i slightly and transiently. The reintroduction of Ca²⁺ induced a transient increase followed by a sustained increase in [Ca²⁺]_i. An increase of [K⁺]_o (151 mM) abolished the [Ca²⁺]_i increase following the reintroduction of Ca²⁺. b IM (5 μM). The addition of 5 μM IM in the Ca²⁺-free solution increased [Ca²⁺]_i transiently. The reintroduction of Ca²⁺ induced a sustained increase in [Ca²⁺]_i. The final [Ca²⁺]_is were much higher than that of 1 μM IM. An increase of [K⁺]_o (151 mM) still increased [Ca²⁺]_i following the reintroduction of Ca²⁺, although the final [Ca²⁺]_i decreased by 10%. c, d Effects of 1 or 5 μM IM on internal Ca²⁺ stores. The addition of 1 or 5 μM IM increased [Ca²⁺]_i transiently, and then the further addition of 10 μM ACh did not induce any [Ca²⁺]_i increase. The reintroduction of Ca²⁺ increased [Ca²⁺]_i