Membrane current responses to externally-applied ATP in the longitudinal muscle of the chicken rectum.
1. Membrane current responses to ATP in enzymically-dispersed single smooth muscle cells from the chicken rectum were investigated by the whole-cell voltage clamp technique. 2. In cells dialysed with a KCl-rich solution under voltage clamp at a holding potential of -40 mV, ATP (10 microM) produced an inward current followed by an outward current. When the holding potential was changed to 0 mV and -80 mV, the biphasic current response to ATP was converted to an outward current alone and an inward current alone, respectively. 3. External application of tetraethylammonium (TEA, 5 mM), intracellular dialysis with a CsCl-rich solution, or inclusion of EGTA (10 mM) in the pipette abolished the outward current response to ATP. 4. Neither depletion of Ca2+ store with caffeine (10 mM) nor block of voltage-gated Ca2+ channels with nifedipine (10 microM) affected the biphasic current response to ATP. After removal of the extracellular Ca2+ the outward current response to ATP was abolished. 5. alpha,beta-methylene ATP (100 microM) elicited a current similar to the ATP-induced current. In the presence of alpha,beta-methylene ATP (100 microM), application of ATP (100 microM) was without effect. 6. In CsCl-filled cells, ATP analogues elicited an inward current and the order of potency was ATP not equal to alpha, beta-methylene ATP > ADP >> AMP. 7. Inclusion of GTP gamma S (0.2 mM) or GDP beta S (2 mM) in the pipette did not affect the ATP-induced inward current in CsCl-filled cells. The reversal potential of the ATP-induced inward current was about 0 mV and was completely inhibited after replacement of the cations in the bath solution by Tris. The reversal potential remained almost unchanged after replacement of Na+ in the bath solution with 1 10 mM Ca2+, but shifted in the negative direction after replacement of Na+ or both Na+ and Ca2+ with glucosamine.8. The results suggest that ATP acts on P2 purinoceptors to cause activation of cation channels with selectivity for Ca2+ over Na+. Moreover, it appears that no G-protein-mediated mechanism is involved and increased Ca2+ entry through the cation channels causes activation of Ca2+-activated K+ channels.
Matsuoka
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T
Department of Veterinary Science, Faculty of Agriculture, Gifu University, Japan.
Komori
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S
Ohashi
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H
D000255:Adenosine Triphosphate / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000187:drug effects; D002586:Cesium / Q000494:pharmacology; D002645:Chickens; D002712:Chlorides / Q000494:pharmacology; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000166:cytology / Q000187:drug effects*; D015221:Potassium Channels / Q000187:drug effects; D011189:Potassium Chloride / Q000494:pharmacology; D012007:Rectum / Q000166:cytology / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
D015220:Calcium Channels; D002712:Chlorides; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D002586:Cesium; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D011189:Potassium Chloride; C023427:guanosine 5'-O-(2-thiodiphosphate); D000255:Adenosine Triphosphate; D019204:GTP-Binding Proteins; C028019:cesium chloride; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium