gms | German Medical Science

Question: One of the important questions about the lower vertebrate heart is whether it possesses conduction tissue comparable with that of higher vertebrates. The aim of our work was to perform the mapping of action potentials of cells in the right atrium of lizard heart.

Method Used: European common lizards(n=12), Lacerta vivipara, weighting 1.9-4.0 g, of both sexes were used. Isolated spontaneously contracting preparations of lizard heart were superfused in tissue bath at temperature 25±1°C with an aerated Ringer solution. The action potentials(APs) were recorded in subendocardial area of right atrium with conventional glass microelectrodes.

Results: Three main types of APs were registered in subendocardial area of right atrium: APs of pacemaker cells, APs of working myocardium cells and APs of conducting cells. Action potentials of pacemaker cells were recorded from the base of sinoatrial and atrioventricular valves. The maximal depolarization rate of sinoatrial pacemaker cells was 6.4±0.9 V/sec. Action potentials of conducting cells had distinct phase of early fast repolarization and phase of plateau. Conducting cells generated APs with the larger value of maximal depolarization rate (60±6 V/sec vs. 28±4 V/sec) as compared to contractile cells. Action potentials of conducting cells are usually recorded at the distance of about 1000 µm from cranial end of sinoatrial orifice (moving a microelectrode in anterograde direction toward the base of atrioventricular valve).

Conclusion: We thus conclude that the conducting cells present in the lizard right atrium.