| Summary: | Fast sodium current (INa) provides depolarization of working myocardium and defines the excitability of its cells and the velocity of excitation propagation in the tissue. Alterations in activation and inactivation of INa channels can lead to the onset of various arrhythmias. Cardiac INa is poorly studied in most vertebrate animals (excepting mammals) – including birds which are of great interest for comparative physiology. In the present work we for the first time study the characteristics of fast sodium current in myocardium of adult bird. Using standard patch clamp method, we recorded INa in isolated atrial and ventricular cardiomyocytes of Japanese quail. The current had great amplitude and quickly recovered from inactivation both in atrial and ventricular cells; the fast inactivation time constant of INa in atrial cells was lower than that of ventricular cells. Steady-state activation and inactivation suggest that sodium window current in avian myocardium is less pronounced in comparison to that in mammalian heart. In quail ventricular myocytes the blocker of late sodium current ranolazine caused a slight decrease in peak current amplitude and did not affect inactivation – however, it shifted steady-state inactivation curve towards more negative potentials, shortened action potentials and caused a decrease in maximum upstroke velocity. Thus, the characteristics of INa in quail myocardium reflect an adaptation to high heart rates in birds, and also suggest possible differences in the structure and function of INa channels between birds and mammals. Быстрый натриевый ток (INa) обеспечивает деполяризацию рабочего миокарда, определяя возбудимость его клеток и скорость распространения возбуждения. Нарушения активации и инактивации каналов натриевого тока могут приводить к развитию различных аритмий. У большинства позвоночных, за исключением млекопитающих, INa исследован достаточно слабо – в том числе и у птиц, представляющих большой интерес для сравнительной физиологии. Данная работа впервые рассматривает ...
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