[Glomus cell in controlling vascular tone of the carotid labyrinth (Xenopus laevis)]

To clarify the physiological significance of g-s connection (intimate apposition of the glomus cell to the smooth muscle), vascular responses of the carotid labyrinth to both catecholamines and chemoreceptor stimulants were investigated using Xenopus laevis. The results obtained were as follows. Density of dense-cored vesicles in the glomus cell was significantly varied in three different parts of the cytoplasm (N, M, P). In the part of the cytoplasm containing the nucleus (N) the density was lowest, and in the processes (P) it was highest. This bias in distribution was intensified by efferent stimulation of the glossopharyngeal nerve. In the artificially perfused labyrinth, the administration of catecholamines (adrenaline, noradrenaline and dopamine) decreased the outflow of the internal carotid artery in many cases. In a few cases it increased the internal outflow. Phentolamine changed the decrease of the outflow to an increase, while propranolol changed the increase to decrease. Acetylcholine strongly reduced the internal outflow. This response was depressed by atropine, hexamethonium and phentolamine, while intensified by propranolol. Sodium cyanide reduced the internal outflow. This effect was depressed by phentolamine. The possibility that the glomus cell participates in controlling the blood flow of the labyrinth as a result of the secretion of catecholamine through the g-s connection is discussed.