Intestinal glucose transport and salinity adaptation in a euryhaline teleost
Reshkin, S.J.; Ahearn, G.A.
American Journal of Physiology 252(3 Pt 2): R567-R578
1987
ISSN/ISBN: 0002-9513 PMID: 3826419 Document Number: 293035
Glucose transport by upper and lower intestinal brush-border membrane vesicles of the African tilania (Oreochromis mossambicus) was characterized in fish acclimated to either freshwater or full-strength seawater. D-[3H]-glucose uptake by vesicles was stimulated by a transmembrane Na gradient, was electrogenic, and was enhanced by countertransport of either D-glucose or D-galactose. Glucose transport was greater in the upper intestine than in the lower intestine and in seawater animals rather than in fish acclimated to freshwater. Glucose influx (10-s uptake) involved both saturable and nonsaturable transport components. Seawater adaptation increased apparent glucose influx Kt, Jmax, apparent diffusional permeability (P), and the apparent Na affinity of the cotransport system in both intestinal segments, but the stoichiometry of Na-glucose transfer (1:1) was unaffected by differential saline conditions or gut region. It is suggested that increased sugar transport in seawater animals is due to the combination of enhanced Na-binding properties and an increase in number or transfer rate of the transport proteins. Freshwater animals compensate for reduced Na affinity of the coupled process by markedly increasing the protein affinity for glucose.