Regional differences in effects of 4-aminopyridine within the sinoatrial node

An experiment was conducted to investigate the role of the transient outward current (Ito) in the sinoatrial node by blocking the current with 4-aminopyridine in small ball-like tissue preparations from different regions of the rabbit sinoatrial node. It was shown for the first time ever that 4-aminopyridine-sensitive current plays a significant part in the electrical activity of the sinoatrial node and that this function differs from the periphery to the center and from the superior part of the sinoatrial node to the inferior part.