title: Sulfonylurea and K(+)-channel opener sensitivity of K(ATP) channels. Functional coupling of Kir6.2 and SUR1 subunits.
abstract: The sensitivity of K(ATP) channels to high-affinity block by sulfonylureas and to stimulation by K(+) channel openers and MgADP (PCOs) is conferred by the regulatory sulfonylurea receptor (SUR) subunit, whereas ATP inhibits the channel through interaction with the inward rectifier (Kir6.2) subunit. Phosphatidylinositol 4, 5-bisphosphate (PIP(2)) profoundly antagonized ATP inhibition of K(ATP) channels expressed from cloned Kir6.2+SUR1 subunits, but also abolished high affinity tolbutamide sensitivity. By stabilizing the open state of the channel, PIP(2) drives the channel away from closed state(s) that are preferentially affected by high affinity tolbutamide binding, thereby producing an apparent loss of high affinity tolbutamide inhibition. Mutant K(ATP) channels (Kir6. 2[DeltaN30] or Kir6.2[L164A], coexpressed with SUR1) also displayed an "uncoupled" phenotype with no high affinity tolbutamide block and with intrinsically higher open state stability. Conversely, Kir6. 2[R176A]+SUR1 channels, which have an intrinsically lower open state stability, displayed a greater high affinity fraction of tolbutamide block. In addition to antagonizing high-affinity block by tolbutamide, PIP(2) also altered the stimulatory action of the PCOs, diazoxide and MgADP. With time after PIP(2) application, PCO stimulation first increased, and then subsequently decreased, probably reflecting a common pathway for activation of the channel by stimulatory PCOs and PIP(2). The net effect of increasing open state stability, either by PIP(2) or mutagenesis, is an apparent "uncoupling" of the Kir6.2 subunit from the regulatory input of SUR1, an action that can be partially reversed by screening negative charges on the membrane with poly-L-lysine.
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Koster
authors.forename: Q
authors.initials: Q
authors.lastname: Sha
authors.forename: C G
authors.initials: CG
authors.lastname: Nichols
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003981:Diazoxide / Q000494:pharmacology; D004232:Diuretics; D004558:Electric Stimulation; D004594:Electrophysiology; D016695:Glycosyltransferases; D007004:Hypoglycemic Agents / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects* / Q000235:genetics; D054086:KATP Channels; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins; D016296:Mutagenesis; D018408:Patch-Clamp Techniques; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000494:pharmacology; D011107:Polylysine / Q000378:metabolism; D015221:Potassium Channels / Q000819:agonists* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D012097:Repressor Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D029701:Saccharomyces cerevisiae Proteins; D049993:Sodium Chloride Symporter Inhibitors / Q000494:pharmacology; D013453:Sulfonylurea Compounds / Q000494:pharmacology*; D014044:Tolbutamide / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D004232:Diuretics; D007004:Hypoglycemic Agents; D054086:KATP Channels; D008565:Membrane Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D049993:Sodium Chloride Symporter Inhibitors; D013453:Sulfonylurea Compounds; C092520:uK-ATP-1 potassium channel; D011107:Polylysine; D000244:Adenosine Diphosphate; D014044:Tolbutamide; D016695:Glycosyltransferases; C092031:SUR1 protein, S cerevisiae; D003981:Diazoxide