Effects of [Ca2+]i and temperature on minK channels expressed in Xenopus oocytes.

Slowly activating, voltage-dependent minK channels cloned from rat kidney were expressed in Xenopus oocytes. Increase in the bath temperature from 22 to 32 degrees C resulted in a dramatic acceleration of minK channel activation. The extraordinarily high Q10 of minK channel activation was voltage-dependent, being higher at more negative potentials (Q10 at -20 mV; 7.02; at 20 mV: 4.0). While activation of minK channels was highly voltage-dependent at 22 degrees C, voltage had only little effect on minK channel activation at 32 degrees C. Increase in [Ca2+]i which has recently been shown to increase the maximal conductance gmax at room temperature, did not affect gmax at 32 degrees C. However, increase of [Ca2+]i caused acceleration of minK channel activation at both temperatures. The interaction of [Ca2+]i and temperature on gmax and activation rate of minK channels described here is very similar to recent findings on Ca- and temperature-effects on the slowly activating potassium conductance IKs in guinea pig cardiac myocytes.