EFFECTS OF EXTRACELLULAR DIADENOSINE TETRAPHOSPHATE ON ACTION POTENTIALS IN ATRIAL AND VENTRICULAR MYOCARDIUM OF THE RAT HEART DURING EARLY POSTNATAL ONTOGENESIS

Diadenosine tetraphosphate (Ap4A) belongs to a wide group of naturally-derived endogenous purine compounds that have been recently considered as new neurotransmitters in autonomic nervous system. It has been shown that Ap4A induces inhibitory effects and modulate adrenergic control in the heart of adult mammals. Nevertheless, the physiological significance of Ap4A in early postnatal development, when sympathetic innervation remains yet immature, has
not been investigated. The aim of the present study was to elucidate the effects Ap4A on heart bioelectrical activity in early postnatal ontogenesis. Action potentials (AP) were recorded with use of standard microelectrode technique in multicellular isolated right atrial (RA), left atrial (LA) and ventricle (RV) preparations from male Wistar rats at postnatal day 1, 14, 21 and, also, from 60-day animals which were considered as adult. The application of Ap4A caused significant reduction of AP duration in atrial (RA and LA) preparations from rats of all ages. Also, Ap4A caused significant AP shortening in RV preparations from rats of various ages, however, the effect was more pronounced in 21-day and adult rats. Ap4A failed to alter automaticity of RA preparations from rats at postnatal day 1, 14, 21 and weakly decreased spontaneous rhythm in RA preparations from the adult rats. The effect of Ap4A was partially abolished by P2-receptor blocker PPADS in LA preparations from both 21 day and adult rats, while failed to suppress Ap4Acaused AP shortening in preparations from 1- and 14-day animals. Thus, extracellular Ap4A causes shortening of AP both in the atrial and ventricular myocardium in early postnatal ontogenesis and adult rats. The effect of Ap4A depends on age only in ventricular myocardium where it may be attributed with growing contribution of diadenosine polyphosphates to the control of myocardium inotropy.

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