The Effects of α1-Adrenoreceptors’ Activation in the Interatrial Septum of Newborn and Adult Rats

详细

Bioelectrical properties of various developing fragments of the heart undergo significant changes during pre- and postnatal ontogeny. However, the general pattern of the heart’s structure and the bioelectrical features of various parts of the “mature” heart are specifically determined in the early stages of embryogenesis. Specifically, the presence of myocardium with a phenotype, which is similar to a pacemaker, was revealed in the interatrial septum (IAS) of the mammalian heart using histological methods. However, the electrical activity in this structure remains understudied. The aim of the present study was to examine the capability of the IAS to generate action potentials spontaneously and the effects of adrenergic stimulation on the bioelectrical activity of the IAS. For this purpose, we recorded the resting and action potentials in the multicellular isolated perfused preparations of the IAS and left atrium from the rat heart at the end of day 1 and at day 60 of postnatal life using the standard microelectrode technique. We found that α₁-adrenomimetic phenylephrine (PE) modified the patterns of action potentials in the samples of IAS and the atrial myocardium from the animals of both ages. In the resting samples without any electrical stimulation, PE induced the generation of action potential in the IAS but not in the atrium because of oscillations in the level of cytoplasmic calcium. Application of the inhibitor of hyperpolarization activated current (I_f) ZD 7288 led to a decrease in the rate of slow diastolic depolarization of action potential in the IAS pacemaker cells, a decrease in the frequency, and the appearance of train activity. Thus, in newborn and adult rats, the IAS myocardium generates spontaneous electrical activity. A necessary condition for the occurrence of pacemaker activity is adrenergic stimulation. The capability to generate spontaneous activity is probably associated with the presence of pacemaker current I_f in the IAS cardiomyocytes.