Short-chain fatty acid transport in the intestine of a herbivorous teleost.

Short-chain fatty acid (SCFA) concentrations of intestinal contents from the herbivorous tilapia, Oreochromis mossambicus, were analysed by gas and high-performance liquid chromatography. Concentrations of acetate ranging from 3 to 18 mmol l-1 were found along the full length of the intestinal tract, as were trace amounts of propionate. Characteristics of [3H]acetate transport by the intestinal brush-border membrane were analysed in isolated brush-border membrane vesicles (BBMV). Influx of [3H]acetate into BBMV occurred by apparent anion exchange and was not enhanced by inwardly directed gradients of sodium or potassium, indicating the lack of sodium-dependent coupling for acetate transport. Competition and stimulation studies with various organic and inorganic anions revealed the likelihood of a transport system in which [3H]acetate is exchanged specifically for intracellular bicarbonate or other SCFA. Other anions tested had only limited or negligible effects on [3H]acetate uptake. Kinetic analysis over a concentration range of external acetate from 0.1 to 35 mmol l-1 yielded a carrier transport Km of 6.4 mmol l-1 and a Jmax of 5.3 nmol mg protein-1 10 s-1. Transport of [3H]acetate was not significantly affected by inhibitory drugs specific for anion exchangers. This study suggests that there is a specific antiport system for anions that is shared by bicarbonate and short-chain volatile fatty acids in the intestinal brush-border membrane of this herbivorous teleost.