title: Purinergic activation of spontaneous transient outward currents in guinea pig taenia colonic myocytes.
abstract: Spontaneous transient outward currents (STOCs) were recorded from smooth muscle cells of the guinea pig taenia coli using the whole cell patch-clamp technique. STOCs were resolved at potentials positive to -50 mV. Treating cells with caffeine (1 mM) caused a burst of outward currents followed by inhibition of STOCs. Replacing extracellular Ca(2+) with equimolar Mn(2+) caused STOCs to "run down. " Iberiotoxin (200 nM) or charybdotoxin (ChTX; 200 nM) inhibited large-amplitude STOCs, but small-amplitude "mini-STOCs" remained in the presence of these drugs. Mini-STOCs were reduced by apamin (500 nM), an inhibitor of small-conductance Ca(2+)-activated K(+) channels (SK channels). Application of ATP or 2-methylthioadenosine 5'-triphosphate (2-MeS-ATP) increased the frequency of STOCs. The effects of 2-MeS-ATP persisted in the presence of charybdotoxin but were blocked by combination of ChTX (200 nM) and apamin (500 nM). 2-MeS-ATP did not increase STOCs in the presence of pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid, a P(2) receptor blocker. Similarly, pretreatment of cells with U-73122 (1 microM), an inhibitor of phospholipase C (PLC), abolished the effects of 2-MeS-ATP. Xestospongin C, an inositol 1,4,5-trisphosphate (IP(3)) receptor blocker, attenuated STOCs, but these events were not affected by ryanodine. The data suggest that purinergic activation through P(2Y) receptors results in localized Ca(2+) release via PLC- and IP(3)-dependent mechanisms. Release of Ca(2+) is coupled to STOCs, which are composed of currents mediated by large-conductance Ca(2+)-activated K(+) channels and SK channels. The latter are thought to mediate hyperpolarization and relaxation responses of gastrointestinal muscles to inhibitory purinergic stimulation.
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557, USA.
authors.forename: I D
authors.initials: ID
authors.lastname: Kong
authors.forename: S D
authors.initials: SD
authors.lastname: Koh
authors.forename: K M
authors.initials: KM
authors.lastname: Sanders
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D018999:Charybdotoxin / Q000494:pharmacology; D003106:Colon / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D004963:Estrenes / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D053496:Inositol 1,4,5-Trisphosphate Receptors; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D051036:Large-Conductance Calcium-Activated Potassium Channels; D047028:Macrocyclic Compounds; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000378:metabolism; D009130:Muscle, Smooth / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D010080:Oxazoles / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated; D011760:Pyrrolidinones / Q000494:pharmacology; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D002120:Calcium Channel Agonists; D015220:Calcium Channels; D000697:Central Nervous System Stimulants; D004963:Estrenes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051036:Large-Conductance Calcium-Activated Potassium Channels; D047028:Macrocyclic Compounds; D010080:Oxazoles; D010726:Phosphodiesterase Inhibitors; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D011760:Pyrrolidinones; D018160:Receptors, Cytoplasmic and Nuclear; D018048:Receptors, Purinergic P2; D013873:Thionucleotides; C108644:xestospongin A; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D018999:Charybdotoxin; D012433:Ryanodine; D001030:Apamin; D002110:Caffeine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000255:Adenosine Triphosphate; D002118:Calcium; C008501:2-methylthio-ATP