Description:
<p>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.</p>