Epithelial and mucosal preparations of canine proximal colon in ussing chambers: comparison of responses

A novel epithelial preparation from proximal canine colon, devoid of its underlying muscularis mucosa, was studied in Ussing chambers and its responses to added agonists compared with those of a conventional full mucosal preparation. We assumed that the responses elicited from the former would reflect direct action of agonists on epithelial cells, and from the latter both direct and indirect effects mediated by functioning nerves in the attached submucosal plexus. Responses of the two preparations to tetrodotoxin, ouabain, scorpion venom, and field stimulation were different, the differences being explicable on the basis of functioning nerves in the mucosal preparation. Histamine stimulated both preparations; the increase in short-circuit current seen with the mucosal but not the epithelial preparation was inhibited by tetrodotoxin. Serotonin was a better stimulant of the epithelial preparation. Basal absorptions of both Na+ and Cl- were seen in both mucosa and epithelium, but net absorptions were significantly greater in the latter, suggesting tonic neuronal inhibition of absorption in the mucosa. These two preparations would prove useful in analysing direct and indirect effects of agonists on colonic transport.