[A study of automatic activity and morphology of guinea-pig aortic vestibule]

The automatic activity of aortic vestibule was studied in 82 guinea-pig heart preparations with intracellular microelectrode. Spontaneous activity could be recorded in 16 preparations (19.5%), while in 61 preparations (74.4%) automatic activity could be induced by electrical stimulation. Of these preparations, they were all found a very small region below the right and the poster valves, the response showed a slow and low rising phase and a marked spontaneous depolarization in phase 4. The response could be blocked by Mn2+ and nifedipine. Outside of the specialized valve region, all recorded vestibule action potentials pertain to the fast type. Light and electron microscopic examination showed that the structure of the specialized local aortic vestibule region was similar to that of ordinary myocardium possessing slow automatic activity instead of the ordinary ventricular musculature.