title: Effect of adenosine 5'triphosphate (ATP) on the isolated rectum of the rainbow lizard Agama agama.
abstract: ATP but not adenosine contracts lizard isolated rectal muscles. Theophylline, quinidine, nifedipine and lack of Ca2+ inhibited ATP contractions, but dipyridamole, indomethacin, atropine, D-tubocurarine, phentolamine, L-propranolol, cimetidine, mepyramine and methysergide did not significantly modify the contractions. ATP inhibited Ca2+-induced contractions in Na+-free, high K+ media. In normal Ringer, it relaxed carbachol-contracted muscles and inhibited KCl contractions. The results suggest that ATP contractions are dependent upon external Ca2+, and are probably associated with extracellular Ca+ influx. The contractions appear to have occurred independently of receptor activation and may have been mediated by a depolarising action of the nucleotide. The relaxant effect of ATP possibly occurred as a consequence of inhibition of Ca2+ influx into carbachol or K+-depolarised muscles.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D002122:Calcium Chloride / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D004176:Dipyridamole / Q000494:pharmacology; D066298:In Vitro Techniques; D008116:Lizards; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011802:Quinidine / Q000494:pharmacology; D012007:Rectum / Q000187:drug effects*; D013806:Theophylline / Q000494:pharmacology
chemical_list: D004176:Dipyridamole; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D002217:Carbachol; D013806:Theophylline; D009543:Nifedipine; D011802:Quinidine; D002122:Calcium Chloride; D002118:Calcium