Dietary modulation of intestinal nutrient transport in the teleost fish tilapia

Tilapia (Oreochromis mossambicus) were fed a diet with either 60% carbohydrate (70% grain-4% fish meal) or 17% carbohydrate (11% grain-65% fish meal) for greater than or equal to 4 wk. Intestinal uptake of radiolabeled acetate, D-glucose, and L-proline was measured in brush-border membrane vesicles. As expected, fish fed high carbohydrate had significantly higher D-glucose uptake than those fed low carbohydrate [maximal uptake rate (Vmax), respectively, 84.2 +/- 18.2 vs. 37.4 +/- 10.9 pmol.mg protein-1.s-1; n = 4 batches of vesicles in each case; t test, P less than 0.025]. The change in glucose transport was specific, because in the same batches of vesicles there was no significant diet effect on carrier-mediated uptake of L-proline or acetate. Also as expected, dietary modulation of carrier-mediated transport was effected primarily by alterations in Vmax and not apparent Michaelis constant (Km); Km was not significantly altered by diet for either D-glucose (high carbohydrate vs. low carbohydrate, respectively, 0.34 +/- 0.17 vs. 0.12 +/- 0.03 mM; P greater than 0.2), L-proline (respectively, 0.10 +/- 0.03 vs. mM 0.13 +/- 0.05), or acetate (respectively, 4.8 +/- 1.4 vs. mM 6.5 +/- 2.2).