AVIAN CECUM - ROLE OF GLUCOSE AND VOLATILE FATTY-ACIDS IN TRANSEPITHELIAL ION-TRANSPORT

In the fowl cecum in vitro, the influence of glucose and the three most prevalent naturally occurring volatile fatty acids (acetate, propionate, butyrate) on short-circuit current (I(sc)), electrical resistance, and transport of Na and Cl was determined. When glucose, acetate, or butyrate was present, ion transport was characterized by electrogenic Na absorption, >65% of which was amiloride inhibitable, and Cl secretion, which also was electrogenic. I(sc) could be completely accounted for by net fluxes of Na and Cl. When glucose, acetate, or butyrate (10 mM both sides) was included in the incubation medium, cecal tissue maintained its I(sc) and a constant rate of net Na absorption and Cl secretion for a 5-h period. When no substrate was present or propionate was included in the medium, a marked fall in I(sc) and net Na and Cl fluxes was seen. Glucose caused an increase in I(sc) when added only to the serosal side. As 3-O-methyglucose (not metabolized) was not effective in stimulating I(sc) of the cecum (serosal or mucosal addition), it appeared that glucose increased I(sc) by acting as an energy substrate for active Na transport. Acetate and butyrate appeared to be equally effective in stimulating Na transport and I(sc) when placed on either side of the membrane. When the preparation was supplied with glucose (serosal side) and acetate was added to the mucosal side, no further stimulation of I(sc) occurred. Thus it appeared that acetate and butyrate were acting as substrates for active Na transport rather than stimulating Na transport by some other mechanism such as a cotransport with Na. Aldosterone added at a physiological concentration in vitro caused a marked stimulation of I(sc), Na absorption, and Cl secretion when glucose was supplied as the substrate. Aldosterone stimulation of amiloride-sensitive I(sc) was due to enhancement of Na transport in the mucosal-to-serosal direction.