Demonstration of the localization of muscarinic acetylcholine receptors in the gastric mucosa. Light and electron microscopic autoradiographic studies using 3H-quinuclidinyl benzilate.

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  • LIGHT AND ELECTRON MICROSCOPIC AUTORADIOGRAPHIC STUDIES USING <sup>3</sup>H-QUINUCLIDINYL BENZILATE

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For autoradiographic demonstration of the muscarinic acetylcholine receptor (m-AChR) in the gastric mucosa, 3H-quinuclidinyl benzilate (3H-QNB), a potent muscarinic antagonist, was administered to rats at a constant rate of 1.4ml per hr via an aortic catheter. Fixation of the tissue was made by a freeze-drying procedure, followed by the wet-sectioning of the Epon blocks with ethylene glycol and the dry-mounting of the emulsion to obliterate loss of the water soluble radiolabeled antagonist. To examine the specificity of the autoradiographic reaction, the atropine-treated and the vagotomized rats were also treated in the same manner as the control rats.<br>As a result, it has been confirmed that the parietal cell among the gastric epithelial cells is a major site of labeling of 3H-QNB, whereas few grains are located over the surface epithelium. Some of the grains were also closely associated with the true capillary endothelium in the gastric mucosa. Electron microscopic autoradiography revealed that most of the grains were in close proximity to either the plasma membrane of the parietal cell or the basal plasma membrane of the true capillary endothelium. Preadministration of atropine resulted in a decrease of the labeling of 3H-QNB, whereas the vagotomy caused an increase in the labeling.<br>The above-findings strongly support our hypothesis previously proposed on the basis of the localization of the acetylcholinesterase, that the parasympathetic nerve would have some direct effects on the true capillary as well as on the parietal cell.<br>In addition, the m-AChR was found to be dispersed both on the true capillary endothelium and on the parietal cell plasma membrane by electron microscopic autoradiography, compared with the nicotinic AChR in the neuromuscular junction.

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