[Comparative study of the action of acetylcholine on the transmembrane potentials of the contractile myocardial cells of the ventricles in adult and newborn guinea pigs].

The transmembrane potentials of the contractile myocardium cells of intact heart and their response to acetylcholine were studied in adult and newborn guinea pigs by means of "swimming microelectrodes". High concentration of acetylcholine only slightly reduces the overshoot without causing changes in other parameters of the transmembrane potentials in adult animals whereas in newborn animals acetylcholine induces hyperpolarization of membrane of the contractile myocardium cells, increases the overshoot and the amplitude of the AP. In adult guinea pigs, acetylcholine prevents irreversible fibrillation whereas in newborn animals acetylcholine prevents spontaneous defibrillation.