Purinergic activation of spontaneous transient outward currents in guinea pig taenia colonic myocytes.
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.
Kong
I D
ID
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557, USA.
Koh
S D
SD
Sanders
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KM
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
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