OPENING OF CARDIOVASCULAR ATP-SENSITIVE K+CHANNELS IS INDUCED BY DIMERIZATION OFNUCLEOTIDE-BINDING DOMAINS OF SULFONYLUREARECEPTORS 2A AND 2B

摘要

Cardiac and vascular ATP-sensitive K+ (KAtp) channels are formed from a K channel subunit, Kir6.2 and either sulfonylurea receptor (SUR) 2A or 2B, respectively. SUR is an ABC protein possessing two cytoplasmic nucleotide-binding domains (NBD1 and NBD2). Intracellular ATP and ADP inhibit KAtp channels by interacting with Kir6.2 while activating them through NBDs. The E171Q mutant of MJ0796, a prokaryotic ABC protein which is entirely an NBD, forms an ATP sandwich dimer in the presence of Mg-free, Na-ATP. SUR2A and SUR2B bearing the corresponding mutation in both NBD1 and NBD2 were individually coexpressed with Kir6.2 in HEK293T cells. The formed KATP channels were spontaneously activated in seconds in the presence of intracellular Mg-free, Na- but not K-ATP as measured with the inside-out configuration of the patch-clamp method. This reaction was never observed with wild-type SUR2A/Kir6.2 and SUR2B/Kir6.2 channels. Na-ATP increased the mutant channel activity up to -40 % of the maximum in a concentration-dependent manner. Nicorandil, a Katp channel opener, increased the mutant but not wild-type channel activity in the presence Na-ATP. These results indicate that dimerization of NBD1 and NBD2 is sufficient to induce opening of the SUR2A- or SUR2B-containing KATP channels