Abstract 1011: SUR2 Short Form-Based Channels Confer A Glibenclamide Insensitive, ATP-Sensitive Potassium Current In Cardiac Myocytes
KATP channels are widely distributed in various tissues and play important physiological roles in regulating insulin secretion in pancreatic beta-cells, providing ischemic protections to the heart and modulating vascular tone in smooth muscles. It is generally agreed that the sarcolemmal KATP is a hetero-octamer consisting of a Kir6.0 pore and a sulfonylurea receptor (SUR). A SUR2 mutant mouse was generated by disrupting the first nucleotide-binding domain (NBD1), where a previously reported N-end component for the glibenclamide action site was located. In ventricular myocytes isolated from relatively young mutant mice, a novel ATP-sensitive current (IKATPn) was detected in 33% single-channel recordings with an average amplitude of 12.3 ± 5.4 pA per patch (n = 15), which was 1/4 of the conventional IKATP (55.4 ± 10.0 pA, n = 19). The IC50(ATP) for KATPn was 10 μM compared to 39.3 μM for the conventional KATP suggesting that KATPn could respond faster to low-ATP conditions. Mean burst duration for KATPn (20.6 ± 1.8 ms, n=4) was half of that for the conventional KATP (44.2 ± 9.5 ms, n=4). KATPn was insensitive to 10 μM glibenclamide and could not be re-activated by 0.1– 0.5 mM pinacidil in the presence of ATP. Newly designed SUR2-isoform or variant-specific antibodies identified several novel SUR2 short forms in the sizes of 28 – 68 kDa in addition to a 150-kDa long form in a purified WT cardiac membrane fraction. The 150-kDa long form was absent in the mutant as expected but the SUR2 short forms remained intact. We hypothesized that channels constituted by these short forms, presumably lacking NBD1, confer IKATPn. The SUR2 short forms co-immunoprecipitated with Kir6.0 suggesting that the short forms may function like hemi-transporters reported in other ATP-binding cassette transporter families. Our results show that different KATP compositions based on the novel SUR2 short forms may exist in cardiac sarcolemmal membrane.