α1-Adrenoreceptors’ activation effects in the interatrial septum myocardium in newborn and adult rats

The bioelectric properties of various forming parts of the heart undergo significant changes during pre- and postnatal ontogenesis. Nevertheless, the early stages of embryogenesis determine not only the general scheme of the structure of the heart, but also the features of bioelectric activity in various parts of the mature heart. In particular, the presence of a myocardium with is similar to pacemaker was shown by histological methods in the interatrial septum (AS) of the mammalian heart. However, the electrical activity in this structure remains unexplored. The purpose of this work was to study the ability of AS to generate spontaneous action potentials (AP), as well as to study the effects of adrenergic effects on the bioelectric activity of heart AS. For this, the resting potential and AP were recorded using standard microelectrode techniques in multicellular perfused isolated AS and left atrium preparations obtained from the rat heart at the end of the first day of postnatal development, as well as on the 60th day of life. In our work, α1-adrenomimetic phenylephrine (PE affected the configuration of AP in both AS and atrial tissue obtained from animals of both age groups. In addition, in dormant preparations, PE caused spontaneous activity in AS, but not in atrium, which may be due to fluctuations in the level of cytoplasmic calcium. With the application of a blocker current, activated by hyperpolarization (If), ZD7288 against the background of PE, showed us a decrease in the rate of slow diastolic depolarization of AP in AS - pacemaker cells, a decrease in frequency and the appearance of burst activity, up to complete suppression of AP generation. Thus, the myocardium of the AS in newborn rats generates spontaneous electrical activity in the absence of adrenergic stimulation, which in adult rats is a necessary condition for the appearance of the AS-pacemaker activity. The ability for spontaneous activity is highly – likely to be associated with the presence of pacemaker current If in cardiomyocytes of AS.

heart, interatrial septum, pacemaker, bioelectric activity, action potential, postnatal development

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