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