ABSTRACT
There are important post-natal developmental changes in the heart: as compared to the in the adult, the intrinsic heart rate is slower, the sinoatrial node [SAN] and ventricular action potentials are longer. However, little is known about post-natal developmental changes in the electrophysiological properties of the atrioventricular node [AVN]. The aim of this study was to investigate the differences in the electrophysiological properties of the AVN in the neonate [2-7 days of age] and adult [6 months of age] New Zealand White rabbits. Extracellular potential was recorded from isolated spontaneously beating AVN preparations from neonate and adult rabbits under control conditions and after the application of ion channel blocker s. A VN cycle length was significantly longer in adult as compared to neonate. 2 mM cesium Cs, an If blocker] and 100 nM tetrodotoxin [TTX, a TTX-sensitive neuronal I[na] blocker] significantly increased adult AVN cycle length with almost no effect on neonatal AVN cycle length. In contrast, 5 mM 4-aminopyridine [4-AP, a blocker of I[10]] significantly reduced adult AVN cycle length. Moreover, 2 mM C.v increased while 100 nM TTX almost didn't change and 5 mM 4-AP decreased the difference in cycle length between the neonate and adult rabbit. It can be concluded that there is post-ntitul developmental differences in the electrophysiological properties of the AVN that could speculate differences in the underlying currents and that 4-AP-sensitive currents may be partly responsible for the difference in cycle length between the neonate and adult rabbit