Diverse Cholinergic Receptors in the Cat Carotid Chemosensory Unit
Decades of studies have shown the presence of neurotransmitters in the glomus cell, the putative chemosensory cell, and the involvement of neurotransmitters in carotid body chemotransmission (Gonzalez et al, 1994). We have been proposing that ACh is a major excitatory neurotransmitter in the cat carotid body (Fitzgerald, 2000). ACh fulfills most of criteria as an excitatory neurotransmitter in the carotid body. Regarding the presence of cholinergic receptors, our immunohistological study has shown that α7 subunits of nicotinic ACh receptors (nAChRs) locate at chemoreceptor nerve endings (Shirahata et al, 1998), and that α4 and β2 subunits of nAChRs in glomus cells (Ishizawa et al, 1994). Expression or localization of other subunits of nAChRs or subtypes of muscarinic ACh receptors (mAChRs) has not yet been known. Neuronal nAChRs are ligand-gated cation channels. They are composed of two a (a2-6) and three β (β2-4) subunits, or of five a (a7-9) subunits. Among variable combinations, α3β4, α4β2, and a7 types appear to be the major nAChRs, and they are widely but distinctively expressed in the nervous system (Lukas et al, 1999). Muscarinic AChRs are pharmacologically and molecular biologically classified into 5 subtypes (M1-M5). They are distributed in the nervous system, smooth muscles and gland (Caulfield and Birdsall, 1998). The purpose of the current study is to investigate the gene expression of major cholinergic receptors and to localize the receptor proteins in the cat chemosensitive unit (the carotid body and the petrosal ganglion).
KeywordsCarotid Body Cholinergic Receptor Glomus Cell nAChR Subunit Partial cDNA Sequence
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