Carotid body glomus cells: chemical secretion and transmission (modulation?) across cell-nerve ending junctions.

Glomus cells of the carotid body contain and secrete chemicals during 'natural' stimulation (hypoxia, hypercapnia and acidity), thus, the birth of the 'transmitter hypothesis of chemoreception'. Released chemicals would cross the synaptic cleft between glomus cells and carotid nerve terminals to depolarize the nerve ending membrane during excitation and hyperpolarize the membrane during inhibition. The main problem with this hypothesis is that specific synaptic blockers modify but do not block the effects of natural stimulation, while blocking the effects of the putative transmitters. It is proposed in this review that the secretion of chemicals is modulated by changes in electric coupling between glomus cells and that glomus cell-nerve ending transmission is not blocked by specific blockers for two reasons. One is that multiple transmitters are released. The other, and more the likely explanation, is that there are electric connections between these elements allowing the flow of currents that are unaffected by the blockers.