[Effect of macroergic nucleotides and lysolecithin on the cholinergic reception of the heart muscle in the frog Rana temporaria].

In experiments on isolated frog ventricle, it has been demonstrated that the dose-response curve for negative inotropic reaction of the myocardium to acetylcholine exhibits a sigmoid form, Hill's coefficient (nH) of this reaction being more than 1. The value of nH depends on the interval from isolation of the ventricle and on the duration of perfusion of the latter with Ringer's solution. It was shown that ATP, UTP, UDP and GTP in physiological concentrations induce both the increase in nH and the increase of K50 (acetylcholine concentration evoking the effect which is equal to half of the maximal one) of the investigated physiological reaction. Similar effects are produced by lysolecithin. Possible causes of "physiological cooperativity" of negative inotropic reaction of the myocardium to acetylcholine and the role of energy-rich nucleotides in this process are discussed.