Extracellular NAD⁺ Suppresses Adrenergic Effects in the Atrial Myocardium of Rats during the Early Postnatal Ontogeny

The effects of sympathetic cotransmitter NAD+ (10 μM) on bioelectric activity of the heart under conditions of adrenergic stimulation were studied on isolated spontaneously contracting preparations (without stimulation) of the right atrium from 2-7-day-old rats. Action potentials were recorded in the working myocardium using standard microelectrode technique. Perfusion of the right atrium with norepinephrine solution (1 μM) altered the configuration and significantly lengthened the action potentials. NAD ⁺ against the background of norepinephrine stimulation significantly decreased the duration of action potentials, in particular, at 25% repolarization. The effect of purine compounds NAD ⁺ , ATP, and adenosine on bioelectrical activity of the heart of newborn rats was studied under basal conditions (without norepinephrine stimulation). The effect of NAD ⁺ against the background of adrenergic stimulation was more pronounced than under basal conditions and was probably determined by suppression of I_CaL, which can be the main mechanism of NAD ⁺ action on rat heart.