Carotid body gap junctions: secretion of transmitters and possible electric coupling between glomus cells and nerve terminals.

It is proposed that intercellular coupling between glomus cells and carotid nerve terminals form an integral part of the chemoreceptor process. Coupling is possible because gap junctions occur between these elements. At rest, most glomus cells would be coupled. Stimuli uncouple (or reduce coupling) most glomus cells that extrude their contents toward the nerve terminals. However, other glomus cells do not secrete but recharge and intercellular coupling increases. These phenomena would allow for sustained chemoreceptor activity during prolonged stimulation. Coupling between glomus and sustentacular cells may explain why the behavior of glomus cells in the intact carotid body and when clustered in cultures (when their sustentacular envelope is preserved) is different from that of isolated cells where sustentacular cells are destroyed. The presence of electric synapses between glomus cells and nerve terminals may explain the poor performance of synaptic blockers on natural (hypoxia, hypercapnia, acidity) carotid body stimulation.