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 (I(sc) 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 I(sc) whereas serosal solutions of 1 mM hexamethonium or 1 mM nicotine did not. Addition of a membrane-permeable analogue of cAMP also reduced I(sc) and, in the presence of this analogue, the decrease in I(sc) 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 I(sc) induced by ACh may involve the inhibition of Ba2+-inhibitable K+ currents, as the addition of 100-mu-M BaCl2 to the serosal solution inhibited I(sc) 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.