Electrical properties of chemoreceptor elements in the carotid body

Abstract

The electrical properties of chemoreceptor afferent nerve fibers and glomus cells and the behavior of cytosolic Ca(2+) in glomus cells are reviewed. While this has not been confirmed, spontaneously depolarizing potentials (SDPs) recorded in a chemoreceptor afferent terminal may be the postsynaptic expression of presynaptic events. Glomus cells, which are presynaptic elements, either depolarized or hyperpolarized in response to natural and chemical stimulation. After-hyperpolarization following an initial depolarization and after-depolarization following an initial hyperpolarization were often seen. When a glomus cell depolarizes, voltage noise increases despite a decrease in input resistance in both intact and denervated carotid bodies. The voltage noise may be "receptor noise" generated in the glomus cell itself. The electrical properties of glomus cells change in the denervated carotid body, which suggests that the chemoreceptor afferent nerve exerts some trophic effect(s) on glomus cells. Hypoxia either increases or decreases cytosolic Ca(2+), while ACh or NaCN induces either an increase or no change in cytosolic Ca(2+) in glomus cells. There are at least two possible explanations for voltage changes in glomus cells: a chemical stimulus first depolarizes the glomus cell and induces Ca(2+) influx to release chemical substances, or a chemical stimulus induces an increase in [Ca(2+)](i) and then hyperpolarizes the glomus cell via potassium influx.

Cellular mechanisms involved in CO2 and acid signaling in chemosensitive neurons

“…There are several recent reviews of various aspects of the function of, and signaling in, carotid body cells (147,163,212,241). The carotid body, the primary site of peripheral chemoreception, has two types of cells: catecholamine-containing type I cells (glomus cells) and type II cells (sustentacular cells), which are like glial cells.…”

Responses of glomus cells to hypoxia and acidosis are uncoupled, reciprocal and linked to ASIC3 expression: selectivity of chemosensory transduction

“…We could therefore conclude that despite the presence of symmetrical junctions (desmosomes) between glomus cells (Hess, 1975; Abudara et al . 2002; Hayashida & Hirakawa, 2002) the electrogenic coupling that might have been expected to unify the response possibly in all the cells of the same cluster did not take place.…”

Carotid chemoreceptor “resetting” revisited

“…Although most studies have found that glomus cell [Ca 2+ ] i increases as P O 2 is lowered, some have reported that a substantial proportion of glomus cells do not respond to hypoxia (Bright et al, 1996; Hayashida and Hirakawa, 2002). A common feature of these studies is the use of mild hypoxia challenge (superfusate P O 2 ~ 35–38 mmHg) which, based on the [Ca 2+ ] i - P O 2 relationship from multiple studies, would be expected to cause either a small or no [Ca 2+ ] i rise in dissociated glomus cells (Fig.…”

“…Four studies have reported that [Ca 2+ ] i may increase or decrease in response to hypoxia in glomus cells from adult rat or mouse (Donnelly and Kholwadwala, 1992; Hayashida et al, 2000; Wotzlaw et al, 2011; Zhang and Eyzaguirre, 1999). One of these studies employed imaging of glomus cells in-situ in the intact, adult mouse CB and the other used minimally-disrupted clusters of glomus cells from adult rats, suggesting that [Ca 2+ ] i responses of glomus cells in-situ may differ from dissociated cells (Hayashida and Hirakawa, 2002; Hayashida et al, 2000; Wotzlaw et al, 2011). Further study will be required to determine whether such heterogeneity of glomus cell [Ca 2+ ] i responses is characteristic of the adult, associated with to cell-cell interactions or related to methodology or other factors.…”