Differences in the mechanism of metabolic regulation of ATP-sensitive K+ channels containing Kir6.1 and Kir6.2 subunits.
OBJECTIVE
ATP sensitive K(+) channels (K(ATP)) sense adenine nucleotide concentrations and thus couple the metabolic state of the cell to membrane potential. The hetero-octameric complex of a sulphonylurea receptor (SUR2B) and an inwardly rectifying K(+) channel (Kir6.1) and the corresponding native channel in smooth muscle are relatively insensitive to variations in intracellular ATP. Activation of these channels in blood vessels during hypoxia/ischaemia is thought to be mediated via hormonal regulation such as cellular adenosine release or the release of mediators from the endothelium. In contrast, intracellular ATP prominently inhibits Kir6.2 containing complexes, such as those present in cardiac myocytes. Thus, we investigated differences in the mechanism of metabolic regulation of Kir6.1 and Kir6.2 containing K(ATP) channels.


RESULTS
We have heterologously expressed K(ATP) channel subunits in HEK293 and CHO cells and studied their function using (86)Rb efflux and patch clamping. We show that rodent Kir6.1/SUR2B has direct intrinsic metabolic sensitivity independent of any regulation by protein kinase A. In contrast to Kir6.2 containing complexes, this was not endowed by the ATP sensitivity of the pore forming subunit but was instead a property of the SUR2B subunit. Mutagenesis of key residues within the nucleotide-binding domains (NBD) implicated both domains in governing the metabolic sensitivity.


CONCLUSIONS
Kir6.1\SUR2B has intrinsic sensitivity to metabolism endowed by the likely processing of adenine nucleotides at the NBD of SUR2B.
BHF Laboratories, Department of Medicine, The Rayne Institute, University College London, Room 107, 5 University Street, London WC1E 6JJ, UK.
Tabasum
T
Farzaneh
Andrew
A
Tinker
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000227:Adenine Nucleotides / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004734:Energy Metabolism; D006801:Humans; D054086:KATP Channels / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011955:Receptors, Drug / Q000235:genetics / Q000378:metabolism*; D012414:Rubidium Radioisotopes; D064233:Sulfonylurea Receptors; D013997:Time Factors; D014162:Transfection; D000099161:Kcnj11 Channel
D018528:ATP-Binding Cassette Transporters; D000227:Adenine Nucleotides; D054086:KATP Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D012414:Rubidium Radioisotopes; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel; C092520:uK-ATP-1 potassium channel