Identification of muscarinic acetylcholine receptors in isolated canine lingual epithelia via voltage clamp measurements.
Acetylcholine (ACh), muscarine and methacholine all decreased the short-circuit current (Isc) measured across isolated canine lingual epithelia bathed in symmetrical solutions of Krebs-Henseleit buffer when added to the serosal, but not mucosal, solutions. Atropine inhibited the ACh-induced decrease in Isc whereas serosal solutions of 1 mM hexamethonium or 1 mM nicotine did not. Addition of a membrane-permeable analogue of cAMP also reduced Isc and, in the presence of this analogue, the decrease in Isc produced by ACh was markedly reduced. These data suggested the presence of muscarinic acetylcholine receptors in the serosal membranes of isolated canine lingual epithelia. The decrease in Isc induced by ACh may involve the inhibition of Ba(2+)-inhibitable K+ currents, as the addition of 100 microM BaCl2 to the serosal solution inhibited Isc and also completely inhibited the response produced by ACh. These findings suggest that responses of sensory fibres in lingual epithelia elicited by ACh may involve an interaction of ACh with epithelial cells rather than a direct interaction of ACh with receptors on sensory nerves.
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