[Identification of rat sinus node pacemaker cells by intracellular injection of lanthanum ions]

Action potentials of pacemaker cells were recorded on an isolated preparation of rat right atrium. Lanthanum ions were injected via a recording microelectrode. The sinus node area was treated for electron microscopy. The electron-dense clusters of lanthanum ions were identified in pacemaker cell organelles, such as cytoplasmic and mitochondrial matrix, external membrane of mitochondria, and inner surface of cytolemma. Treatment with La3+ produced no significant alterations in cellular morphology.