[Morphophysiological organization of the sinoatrial node of the rat heart].

A combined morphophysiologic study of the rat heart sinus node pacemaker cells showed this conductive formation to comprise true and latent pacemakers. The latent pacemaker cell population is heterogeneous in terms of electric activity as well as morphology. The electrophysiologic and morphologic characteristics of latent pacemaker cells undergo a smooth change from centre to periphery of the sinus node. No criteria could be identified for accurate correlation of morphologic and electrophysiologic characteristics of sinus node pacemaker cells, not even by intracellular labelling of cardiomyocytes that belonged to definite electric activity types. The differences between these cells are assumed to be largely related to specific membrane structures, such as ion channels and receptors.