Residual Calcium Ions Depress Activation of Calcium-Dependent Current

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Abstract
Calcium ions enter and accumulate during depolarization of some cells, activating a potassium current, I K(Ca) , that depends on the cytoplasmic concentration of calcium ions, [Ca] i . However, elevation of [Ca] i can depress I K(Ca) elicited by a subsequent membrane depolarization. The depression of I K(Ca) is ascribed here to a [Ca] i -mediated inactivation of the voltage-gated calcium conductance, which causes a net reduction in calcium ions available for the activation of I K(Ca) . This suggests that other processes dependent on gated calcium entry may also be depressed by small background elevations in cytosolic free calcium ions.