Possible role of coupling between glomus cells in carotid body chemoreception.

Glomus cells of the carotid body are dye and electrically coupled due to the presence of gap junctions between them. During stimulation by hypoxia, hypercapnia and acidity, about 70% of the cells uncouple to various degrees, whereas the rest either develop tighter coupling or are unaffected. Similar results have been obtained with exogenous administrations of naturally present transmitters such as dopamine and cholinergic substances. Uncoupling is associated with a decrease in junctional conductance and closing of intercellular channels. Tighter coupling is accompanied by opposite effects on these parameters. We think that cell isolation uncoupling leads to release of larger amounts of transmitters toward the carotid nerve sensory terminals. Tighter coupling would reduce the quantities of released chemicals. We may have a delicate titration process modulating the sensory discharge frequency, since a single sensory fiber divides to innervate up to 20 glomus cells. Thus, the discharge frequency of this fiber (the sensory unit) will result from the contributions of its many branches, each impinging on variously active glomus cells.