Level of expression controls modes of gating of a K+ channel

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Abstract
Several distinct subfamilies of K+ channel genes have been discovered by molecular cloning, however, in some cases the structural differences among them do not account for the diversity of K+ current types, ranging from transient A‐type to slowly inactivating delayed rectifier‐type, as members within each subfamily have been shown to code for K+ channels of different inactivation kinetics and pharmacological properties. We show that a single K+ channel cDNA of the Shaker subfamily (ShH4) can express in Xenopus oocytes not only a transient A‐type K+ current but also, upon increased level of expression, slowly inactivating K+ currents with markedly reduced sensitivity to tetraethylammonium. In correlation with the macroscopic currents there are single‐channel gating modes ranging from the fast‐inactivation mode which underlies the transient A‐type current, to slow‐inactivation modes characterized by bursts of longer openings, and corresponding to the slowly inactivating macroscopic currents.