Revisiting the role of Ca2+ in Shaker K+ channel gating

Shaker K+ channels were expressed in outside-out macropatches excised from Xenopus oocytes, and the effects on gating of removal of extracellular Ca2 were examined in the complete absence of intracellular divalent cations. R emoval of extracellular Ca2+ by perfusion with EDTA-containing solution cau sed a small negative shift in the channel's voltage-activation curve and le d to an increased nonselective leak, but did not otherwise alter or disrupt the channels. The results contradict the proposal that Ca2+ is an essentia l component required for maintenance of ion selectivity and proper gating o f K-v-type K+ channels. The large nonselective leak in Ca2+-free conditions was found to be a patch-seal phenomenon related to F- ion in the recording pipette.