title: Inhibition by purines of the inotropic action of isoprenaline in rat atria.
abstract: The effects of a series of adenosine derivatives were examined on the catecholamine-stimulated electrically-driven rat left atrium in vitro. All the purines tested reduced the positive inotropic action of isoprenaline, 0.1 microM, with the potency order: L-N6-phenlylisopropyladenosine (L-PIA) greater than 5'-N-ethylcarboxamide adenosine (NECA) greater than D-PIA greater than 2-chloroadenosine greater than adenosine. Dipyridamole did not change the IC50 of adenosine. The adenosine deaminase inhibitor, 2'deoxycoformycin, produced a small but nonsignificant shift to the left of the adenosine concentration-response curve. The cardiac depressant effects of these purines were reversed by theophylline and the IC50 values were unchanged in the presence of atropine or in atria taken from reserpine-treated rats. It is concluded that the purine receptor mediating these effects should not be classified on the A1/A2 system. The relationship between functionally characterized purine receptors and those originally defined as modulating adenylate cyclase is discussed.
mesh_terms: D000818:Animals; D004347:Drug Interactions; D004558:Electric Stimulation; D006325:Heart Atria / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000037:antagonists & inhibitors*; D009200:Myocardial Contraction / Q000187:drug effects*; D011687:Purines / Q000494:pharmacology*; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects; D011983:Receptors, Purinergic; D013806:Theophylline / Q000494:pharmacology
chemical_list: D011687:Purines; D011956:Receptors, Cell Surface; D011983:Receptors, Purinergic; D013806:Theophylline; D007545:Isoproterenol