Effect of glucose and hyperosmolality on the electrical characteristics of dog colon mucosa in vivo.

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Abstract
A method was developed to maintain the electrical characteristics of the dog colon mucosa, stable over prolonged periods in vivo. This was achieved by paying special attention to the constancy of the volume of the organ and its intraluminal pressure during perfusion. Intraluminal glucose elicits an increase in transmural potential and short circuit current; this was attributed to the presence of a Na-glucose cotransport process in this tissue. Na replacement by K in the perfusate caused an increase in the transmural potential, whereas mannitol substitution evoked an inversion. These observations are probably the result of diffusion potentials. In the mannitol solution, glucose effectively abolished the negative transmural potential, whereas in the K solution, the effect of the sugar was smaller than in the control. Perfusion of a hyperosmotic solution containing mannitol resulted in the development of streaming potentials across the mucosa. Their magnitude was reduced by addition of 2,4-dinitrophenol or by removal of Na from the perfusate. They were counteracted by replacement of mannitol by glucose. The streaming potentials showed no sign of saturability, reflecting a pronounced hydraulic conductivity of the epithelium. The rapidity of onset of the potential response to glucose was enhanced by increasing the perfusion rate, but the response to hyperosmolality was unaffected. Streaming potentials, diffusion potentials and glucose-evoked potentials are generally considered to be features of the small intestinal mucosa; their existence in the dog colon indicates that this epithelium has more in common with small gut than with the majority of mammalian colons.

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