MINK POTASSIUM CHANNELS ARE HETEROMULTIMERIC COMPLEXES

MinK is a transmembrane protein of 130 amino acids found in the kidney , heart, and vestibular system of mammals. Its expression in Xenopus l aevis oocytes induces a voltage-dependent potassium current similar to that Seen in vivo. Indirect evidence has fueled speculation that func tion requires association of MinK and another protein endogenous to oo cytes and native tissues. In this report, we show that direct covalent modification of an oocyte membrane protein alters properties of the M inK ion conduction pore; modified channels exhibit decreased potassium conduction and increased permeability to sodium and cesium. The modif ying reagents, two membrane-impermeant, sulfhydryl-specific methanethi osulfonate derivatives, react only from the extracellular solution at rates that are determined by the conformational state of the channel. These findings indicate that MinK is intimately associated with an ooc yte protein whose exposure to the external solution changes during cha nnel gating and which acts with MinK to establish ion conduction pore function.