title: Diadenosine tetraphosphate-gating of recombinant pancreatic ATP-sensitive K(+) channels.
abstract: Diadenosine tetraphosphate (Ap4A) has been recently discovered in the pancreatic beta cells where targets ATP-sensitive K(+) (K(ATP)) channels, depolarizes the cell membrane and induces insulin secretion. However, whether Ap4A inhibit pancreatic K(ATP) channels by targeting protein channel complex itself was unknown. Therefore, we coexpressed pancreatic K(ATP) channel subunits, Kir6.2 and SUR1, in COS-7 cells and examined the effect of Ap4A on the single channel behavior using the inside-out configuration of the patch-clamp technique. Ap4A inhibited channel opening in a concentration-dependent manner. Analysis of single channels demonstrated that Ap4A did not change intraburst kinetic behavior of K(ATP) channels, but rather decreased burst duration and increased between-burst duration. It is concluded that Ap4A antagonizes K(ATP) channel opening by targeting channel subunits themselves and by keeping channels longer in closed interburst states.
authors.affiliation: Tayside Institute of Child Health, Ninewells Hospital and Medical School, University of Dundee, Scotland, UK.
authors.forename: S
authors.initials: S
authors.lastname: Jovanovic
authors.forename: A
authors.initials: A
authors.lastname: Jovanovic
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D019556:COS Cells / Q000187:drug effects / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D015226:Dinucleoside Phosphates / Q000378:metabolism* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008024:Ligands; D008164:Luminescent Proteins / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors
chemical_list: D018528:ATP-Binding Cassette Transporters; D015226:Dinucleoside Phosphates; D007202:Indicators and Reagents; D007328:Insulin; D008024:Ligands; D008164:Luminescent Proteins; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D049452:Green Fluorescent Proteins; C020733:diadenosine tetraphosphate; D000255:Adenosine Triphosphate