The pacemaker cell of the sinoatrial node of the rabbit

Rabbit sinoatrial nodes were isolated and studied in an attempt to determine the cell of origin of the true pacemaker potential. Cells of the sinoatrial node of the rabbit giving rise to the characteristic true pacemaker potential were iontophoretically tagged with lanthanum. The lanthanum appeared within the cytoplasm of cells, which morpholigically are "P" cells. The lanthanum appeared as small, amorphous, electron-dense globules. It is concluded from this study that the P or pale cell is the source of the true pacemaker action potential of the sinoatrial node.