ATP modulation of ATP-sensitive potassium channel ATP sensitivity varies with the type of SUR subunit.
ATP-sensitive potassium (K(ATP)) channels comprise Kir and SUR subunits. Using recombinant K(ATP) channels expressed in Xenopus oocytes, we observed that MgATP (100 microm) block of Kir6.2/SUR2A currents gradually declined with time, whereas inhibition of Kir6.2/SUR1 or Kir6.2DeltaC36 currents did not change. The decline in Kir6.2/SUR2A ATP sensitivity was not observed in Mg(2+) free solution and was blocked by the phosphatidylinositol (PI) 3-kinase inhibitors LY 294002 (10 microm) and wortmannin (100 microm), and by neomycin (100 microm). These results suggest that a MgATP-dependent synthesis of membrane phospholipids produces a secondary decrease in the ATP sensitivity of Kir6.2/SUR2A. Direct application of the phospholipids PI 4,5-bisphosphate and PI 3,4,5-trisphosphate in the presence of 100 microm MgATP activated all three types of channel, but the response was faster for Kir6.2/SUR2A. Chimeric studies indicate that the different responses of Kir6.2/SUR2A and Kir6.2/SUR1 are mediated by the first six transmembrane domains of SUR. The MgATP-dependent loss of ATP sensitivity of Kir6.2/SUR2A was enhanced by the actin filament disrupter cytochalasin and blocked by phalloidin (which stabilizes the cytoskeleton). Phalloidin did not block the effect of PI 3,4,5-trisphosphate. This suggests that MgATP may cause disruption of the cytoskeleton, leading to enhanced membrane phospholipid levels (or better targeting to the K(ATP) channel) and thus to decreased channel ATP sensitivity.
Song
D K
DK
University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, United Kingdom.
Ashcroft
F M
FM
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D003572:Cytochalasins / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051379:Mice; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D009355:Neomycin / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010590:Phalloidine / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D011955:Receptors, Drug / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013453:Sulfonylurea Compounds / Q000378:metabolism; D064233:Sulfonylurea Receptors; D013997:Time Factors; D000077191:Wortmannin; D014981:Xenopus
D018528:ATP-Binding Cassette Transporters; C577508:Abcc8 protein, mouse; C577509:Abcc8 protein, rat; C577511:Abcc9 protein, mouse; D000730:Androstadienes; D002867:Chromones; D003572:Cytochalasins; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011500:Protein Synthesis Inhibitors; D011955:Receptors, Drug; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D013453:Sulfonylurea Compounds; D064233:Sulfonylurea Receptors; D010590:Phalloidine; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D000255:Adenosine Triphosphate; D009355:Neomycin; D000077191:Wortmannin