The intrinsic cycle length in small pieces isolated from the rabbit sinoatrial node

In this study we show that small pieces of tissue cut from the intact sinoatrial node beat faster, but with the same regularity as the intact sinoatrial node. The pieces with highest diastolic depolarization rate are not isolated from the primary pacemaker area, but from sites closer to the crista terminalis. In pieces cut from the primary pacemaker area, changes in the action potential configuration are restricted to the action potential duration, whereas in pieces cut from sites closer to the crista terminalis, not only the action potential duration has decreased, but also the diastolic depolarization rate has increased. Under the influence of adrenaline or acetyl-choline, quiescent pieces are able to generate spontaneous activity.