Nicotinic Acetylcholine Receptor Channels in Cat Chemoreceptor Cells
Neurotransmitters are likely to play a key role for hypoxic chemotransmission in the carotid body. Among several neurotransmitters, ACh appears to be a major excitatory neurotransmitter in the cat carotid body (Fitzgerald, 2000). ACh may act directly on the afferent nerve endings and generates action potentials (Hayashida et al., 1980; Zhong & Nurse, 1997). Alternatively, ACh may work through nicotinic ACh receptors (nAChRs) in the carotid body chemosensory cells, glomus cells, and modulate the release of neurotransmitters (Fidone et al., 1990). Our recent data have shown the presence of ¦Á3, ¦Á4, ¦Â2 and ¦Â4, but not ¦Á7, subunits of nAChRs in the cat glomus cells (Hirasawa et al., in this book; Shirahata et al., 1998). Nicotinic AChRs belong to ligand-gated ion channels, that are composed of five receptor subunits. Their subunit compositions categorize nAChRs into three receptor types: (1) muscle type nAChRs, (2) heteromeric type neuronal nAChRs that consist of ¦Á subunits (¦Á2-6) and ¦Â subunits (¦Â2-4), and (3) homomeric type neuronal nAChRs that consist of only a subunits (¦Á7-9). Their stoichiometry and their electrophysiological characteristics depend on the subunit compositions (McGehee & Role, 1995; Lindstrom et al., 1996). Since neuronal nAChR channels are permeable to Ca2+ and Na+ ions, their activation could significantly influence the excitability and fonction of glomus cells. In this study we examined electrophysiological and pharmacological characteristics of nAChRs in glomus cells and infer their role in the excitability of glomus cells.
KeywordsNicotinic Acetylcholine Receptor Carotid Body Glomus Cell Afferent Nerve Ending Major Excitatory Neurotransmitter
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