Electrophysiological evidence for the right atrioventricular pacemaker ring in the reptile heart

Pacemaker atrioventricular (AV) rings, continuous with the AV node, have been shown to be present in the mammalian and avian hearts. There is conspicuous lack of electrophysiological data on the cardiac pacemakers in reptiles. We aimed to characterize the AV ring in the common lizard heart for the first time using conventional microelectrode technique. Detaching the sinoatrial (SA) area unmasked pacemaking in the AV junction. In all seven studied isolated AV ring preparations, we could record action potentials (APs) with characteristic diastolic depolarization, with a slow upstroke (dV/dt _max) of 3.5 ± 0.3 V s^-1 and a low amplitude of 57.8 ± 1.3 mV. The cells with pacemaking potentiality were found to surround the atrial orifice of the right AV valve. We identified some commonalities between phenotype of right AV ring pacemaker APs and SA dominant pacemaker ones. Thus, the AV ring in the reptile heart demonstrates pacemaking activity and contains cells that resemble the electrophysiological characteristics of mammalian and avian pacemaker myocytes in AV rings surrounded the atrial orifices of AV valves.