title: Double-peaked positive chronotropic responses of isolated and cross-perfused dog atria to ATP.
abstract: The effects of a large amount of adenosine and ATP (100 to 3000 micrograms) were investigated on sinus rate and developed tension, using the isolated dog atrium which was perfused with arterial blood from a heparinized donor dog. Each of the substances used for study was administered into the cannulated sinus node artery of the isolated atrium. Adenosine caused monophasic negative chronotropic and inotropic effects in a dose-related manner. However, ATP induced two-peaked positive chronotropic phases during a long-lasting negative chronotropic phase, i.e., initially, brief positive (t-1) effects and secondarily, relatively longer positive chronotropic (t-2) effects. These responses were repetitively induced during the experiment. The t-1 and t-2 were not influenced by treatment with propranolol which significantly blocked the positive chronotropic effect of norepinephrine. Aminophylline treatment significantly suppressed t-2 but not t-1. Quinidine (100-1000 micrograms) did not affect either the t-1 or t-2. It is suggested that ATP-induced tachycardia in the dog is partially due to activation of the P1-purinoceptors named by Burnstock.
mesh_terms: D000241:Adenosine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000628:Aminophylline / Q000494:pharmacology; D000818:Animals; D004285:Dogs; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D010477:Perfusion; D011433:Propranolol / Q000494:pharmacology; D011802:Quinidine / Q000494:pharmacology; D013268:Stimulation, Chemical
chemical_list: D000628:Aminophylline; D000255:Adenosine Triphosphate; D011433:Propranolol; D011802:Quinidine; D000241:Adenosine