Autoradiographic localization of ?-bungarotoxin-binding sites in the carotid body of the rat

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Abstract
Summary Radioiodinated α-bungarotoxin (α-Bgt) was used to localize α-Bgt-acetylcholine receptors in the carotid body of the rat. The gamma spectrometer analyses indicated a high uptake of [125I] α-Bgt in carotid bodies incubated in vitro (1.51 fmole per organ). Incorporation of the isotope was effectively blocked by pretreatment of carotid bodies with d-tubocurarine and unlabeled α-Bgt, but not by atropine. Light microscopic autoradiography showed a heavy labeling of some parenchymal cells. Electron-microscopic autoradiography revealed that labeling was localized along the interface between parenchymal cells, especially where their cytoplasmic processes engage in complex interdigitations. The silver grain counts on electron-microscopic autoradiographs suggest that labelings are preferentially associated with the plasma membrane of certain Type I cells. It is suggested that these Type I cells in the rat's carotid body probably are provided with nicotinic acetylcholine receptors on their plasma membranes.