Molecular Analysis of ATP-sensitive K Channel Gating and Implications for Channel Inhibition by ATP

• DOI: 10.1085/jgp.112.3.333
• Publication Date: 2002-07-26T16:50:20Z
• Authors: Stefan Trapp; Peter Proks; Stephen J. Tucker; Frances M. Ashcroft
• Keywords: Kir6.2; Tolbutamide; Sulfonylurea receptor; Adenosine triphosphate

The β cell KATP channel is an octameric complex of four pore-forming subunits (Kir6.2) and regulatory (SUR1). A truncated isoform Kir6.2 (Kir6.2ΔC26), which expresses independently SUR1, shows intrinsic ATP sensitivity, suggesting that this subunit primarily responsible for mediating inhibition. We show here mutation C166, lies at the cytosolic end second transmembrane domain, to serine (C166S) increases open probability Kir6.2ΔC26 approximately sevenfold by reducing time spends in a long closed state. Rundown activity also decreased. containing C166S markedly reduced sensitivity: Ki from 175 μM 2.8 mM. Substitution threonine, alanine, methionine, or phenylalanine position C166 sensitivity simultaneously increased probability. Thus, does not act as blocker. inhibitory effects tolbutamide are channels composed SUR1 carrying mutation. Our results consistent with idea plays role gating channel, possibly influencing gate located intracellular pore. Kinetic analysis suggests apparent decrease changes other properties, observed when mutated largely consequence impaired transition