Effects of relative hypoxia and hypercapnia on intracellular pH and membrane potential of cultured carotid body glomus cells

H2S generated by the enzyme cystathionine-γ-lyase (CSE) has been implicated in O2 sensing by the carotid body. The objectives of the present study were to determine whether glomus cells, the primary site of hypoxic sensing in the carotid body, generate H2S in an O2-sensitive manner and whether endogenous H2S is required for O2 sensing by glomus cells. Experiments were performed on glomus cells harvested from anesthetized adult rats as well as age and sex-matched CSE+/+ and CSE−/− mice. Physiological levels of hypoxia (Po2 ∼30 mmHg) increased H2S levels in glomus cells, and dl-propargylglycine (PAG), a CSE inhibitor, prevented this response in a dose-dependent manner. Catecholamine (CA) secretion from glomus cells was monitored by carbon-fiber amperometry. Hypoxia increased CA secretion from rat and mouse glomus cells, and this response was markedly attenuated by PAG and in cells from CSE−/− mice. CA secretion evoked by 40 mM KCl, however, was unaffected by PAG or CSE deletion. Exogenous application of a H2S donor (50 μM NaHS) increased cytosolic Ca2+ concentration ([Ca2+]i) in glomus cells, with a time course and magnitude that are similar to that produced by hypoxia. [Ca2+]i responses to NaHS and hypoxia were markedly attenuated in the presence of Ca2+-free medium or cadmium chloride, a pan voltage-gated Ca2+ channel blocker, or nifedipine, an L-type Ca2+ channel inhibitor, suggesting that both hypoxia and H2S share common Ca2+-activating mechanisms. These results demonstrate that H2S generated by CSE is a physiologic mediator of the glomus cell's response to hypoxia.

Download Full-text

Developmental Aspects of Carotid Body Glomus Cells

Histochemistry and Cell Biology of Autonomic Neurons and Paraganglia ◽

10.1007/978-3-642-72749-8_36 ◽

1987 ◽

pp. 208-212

Author(s):

J. T. Hansen

Keyword(s):

Carotid Body ◽

Glomus Cells ◽

Carotid Body Glomus Cells

Download Full-text

Ca2+ Current in Rabbit Carotid Body Glomus Cells Is Conducted by Multiple Types of High-Voltage–Activated Ca2+ Channels

Journal of Neurophysiology ◽

10.1152/jn.1997.78.5.2467 ◽

1997 ◽

Vol 78 (5) ◽

pp. 2467-2474 ◽

Cited By ~ 48

Author(s):

Jeffrey L. Overholt ◽

Nanduri R. Prabhakar

Keyword(s):

High Voltage ◽

Carotid Body ◽

Neurotransmitter Release ◽

Relative Proportion ◽

Sensory Transduction ◽

Arterial Oxygen ◽

Patch Clamp Technique ◽

Simultaneous Application ◽

Glomus Cells ◽

Carotid Body Glomus Cells

Overholt, Jeffrey L. and Nanduri R. Prabhakar. Ca2+ current in rabbit carotid body glomus cells is conducted by multiple types of high-voltage–activated Ca2+ channels. J. Neurophysiol. 78: 2467–2474, 1997. Carotid bodies are sensory organs that detect changes in arterial oxygen. Glomus cells are presumed to be the initial sites for sensory transduction, and Ca2+-dependent neurotransmitter release from glomus cells is believed to be an obligatory step in this response. Some information exists on the Ca2+ channels in rat glomus cells. However, relatively little is known about the types of Ca2+ channels present in rabbit glomus cells, the species in which most of the neurotransmitter release studies have been performed. Therefore we tested the effect of specific Ca2+ channel blockers on current recorded from freshly dissociated, adult rabbit carotid body glomus cells using the whole cell configuration of the patch-clamp technique. Macroscopic Ba2+ current elicited from a holding potential of −80 mV activated at a V m of approximaely −30 mV, peaked between 0 and +10 mV and did not inactivate during 25-ms steps to positive test potentials. Prolonged (≈2 min) depolarized holding potentials inactivated the current with a V 1/2 of −47 mV. There was no evidence for T-type channels. On steps to 0 mV, 6 mM Co2+ decreased peak inward current by 97 ± 1% (mean ± SE). Nisoldipine (2 μM), 1 μM ω-conotoxin GVIA, and 100 nM ω-agatoxin IVa each blocked a portion of the macroscopic Ca2+ current (30 ± 5, 33 ± 5, and 19 ± 3% after rundown correction, respectively). Simultaneous application of these blockers revealed a resistant current that was not affected by 1 μMω-conotoxin MVIIC. This resistant current constituted 27 ± 5% of the total macroscopic Ca2+ current. Each blocker had an effect in every cell so tested. However, the relative proportion of current blocked varied from cell to cell. These results suggest that L, N, P, and resistant channel types each conduct a significant proportion of the macroscopic Ca2+ current in rabbit glomus cells. Hypoxia-induced neurotransmitter release from glomus cells may involve one or more of these channels.

Download Full-text