A mechanism for ATP-sensitive potassium channel diversity: Functional coassembly of two pore-forming subunits

ATP-sensitive potassium channels are an octomeric complex of four pore-form ing subunits of the Kir 6.0 family and four sulfonylurea receptors. The Kir 6.0 family consists of two known members, Kir 6.1 and Kir 6.2, with distin ct functional properties. The tetrameric structure of the pore-forming doma in leads to the possibility that mixed heteromultimers may form. In this st udy, we examine this by using biochemical and electrophysiological techniqu es after heterologous expression of these subunits in HEK293 cells. After t he coexpression of Kir 6.1 and Kir 6.2, Kir 6.1 can be coimmunoprecipitated with isoform-specific Kir 6.2 antisera and vice versa. Coexpression of SUR 2B and Kir 6.2 with Kir 6.1 dominant negatives at a 1:1 expression ratio an d Vice versa led to a potent suppression of current. Kir 6.1, and Kir 6.2 d ominant negative mutants were without effect on an inwardly rectifying pota ssium channel from a different family, Kir 2.1. Single-channel analysis, af ter coexpression of SUR2B, Kir 6.1, and Kir 6.2, revealed the existence of five distinct populations with differing single-channel current amplitudes. All channel populations were inhibited by glibenclamide. A dimeric Kir 6.1 -Kir 6.2 construct expressed with SUR2B had a single-channel conductance in termediate between that of either Kir 6.2 or Kir 6.1 expressed with SUR2B. In conclusion, Kir 6.1 and Kir 6.2 readily coassemble to produce functional channels, and such phenomena may contribute to the diversity of nucleotide -regulated potassium currents seen in native tissues.