title: Small-conductance Ca(2+)-dependent K+ channels activated by ATP in murine colonic smooth muscle.
abstract: The patch-clamp technique was used to determine the ionic conductances activated by ATP in murine colonic smooth muscle cells. Extracellular ATP, UTP, and 2-methylthioadenosine 5'-triphosphate (2-MeS-ATP) increased outward currents in cells with amphotericin B-perforated patches. ATP (0.5-1 mM) did not affect whole cell currents of cells dialyzed with solutions containing ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Apamin (3 x 10(-7) M) reduced the outward current activated by ATP by 32 +/- 5%. Single channel recordings from cell-attached patches showed that ATP, UTP, and 2-MeS-ATP increased the open probability of small-conductance, Ca(2+)-dependent K+ channels with a slope conductance of 5.3 +/- 0.02 pS. Caffeine (500 microM) enhanced the open probability of the small-conductance K+ channels, and ATP had no effect after caffeine. Pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid tetrasodium (PPADS, 10(-4) M), a nonselective P2 receptor antagonist, prevented the increase in open probability caused by ATP and 2-MeS-ATP. PPADS had no effect on the response to caffeine. ATP-induced hyperpolarization in the murine colon may be mediated by P2y-induced release of Ca2+ from intracellular stores and activation of the 5.3-pS Ca(2+)-activated K+ channels.
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno 89557, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Koh
authors.forename: G M
authors.initials: GM
authors.lastname: Dick
authors.forename: K M
authors.initials: KM
authors.lastname: Sanders
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D000666:Amphotericin B / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002478:Cells, Cultured; D003106:Colon / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated; D011336:Probability; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D018048:Receptors, Purinergic P2 / Q000502:physiology; D051640:Small-Conductance Calcium-Activated Potassium Channels; D013873:Thionucleotides / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D018048:Receptors, Purinergic P2; D051640:Small-Conductance Calcium-Activated Potassium Channels; D013873:Thionucleotides; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D001030:Apamin; D004533:Egtazic Acid; D011732:Pyridoxal Phosphate; D000666:Amphotericin B; D000255:Adenosine Triphosphate; D014544:Uridine Triphosphate; C008501:2-methylthio-ATP