AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 6 1568-R1574, Copyright © 1991 by American Physiological Society
Dietary modulation of intestinal nutrient transport in the teleost fish tilapia
E. Titus, W. H. Karasov and G. A. Ahearn
Department of Zoology, University of Hawaii, Honolulu 96822.
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).
