Ontogenic development of lamb intestinal sodium-glucose co-transporter is regulated by diet.
1. The ontogenic development of the intestinal Na(+)-glucose co-transporter was measured in lambs as a function of diet. Transport activity was assayed in brush-border membrane vesicles and the expression of transport protein in the brush-border membrane determined by Western analysis. 2. Na(+)-dependent D-glucose transport increased to a maximum (300-700 pmol mg-1 s-1) within the first 2 weeks of birth and then declined to negligible amounts (less than 10 pmol mg-1 s-1) over the next 8 weeks. There was no further change over the next 2-3 years. Early changes were associated with modifications in both the maximum velocity Vmax for transport and expression of carrier protein in the brush-border plasma membrane. 3. Maintaining lambs on a milk replacer diet beyond the normal weaning period prevented the normal decline in the expression of Na(+)-glucose co-transport. At 5 weeks the transport rate was 433 +/- 150 pmol mg-1 s-1 in lambs maintained on milk replacer, but only 79 +/- 40 pmol mg-1 s-1 in normally reared control lambs. 4. Infusing the proximal intestine of 2- to 3-year-old sheep with 30 mM-D-glucose for four days increased the rate of transport 40- to 80-fold above that found in control animals perfused with mannitol. A similar but smaller increase was observed in one animal perfused with the non-metabolizable sugar alpha-methyl-D-glucopyranoside. The induced increase in glucose transport was correlated with the expression of the co-transporter protein in the brush-border plasma membrane. 5. It is concluded that the age-related decline in Na(+)-glucose co-transport in the sheep intestine is directly due to the decrease in D-glucose (and D-galactose) reaching the small intestine after development of the rumen. These results further suggest that luminal sugar substrates for the co-transporter promote both the maintenance and the up-regulation of the brush-border transport protein and it is the intact sugar itself which controls gene expression during enterocyte maturation.
Shirazi-Beechey
S P
SP
Department of Biochemistry, University College of Wales, Aberystwyth, Dyfed.
Hirayama
B A
BA
Wang
Y
Y
Scott
D
D
Smith
M W
MW
Wright
E M
EM
D000818:Animals; D015153:Blotting, Western; D004032:Diet; D005260:Female; D005947:Glucose / Q000378:metabolism*; D007408:Intestinal Absorption / Q000502:physiology; D007421:Intestine, Small / Q000254:growth & development* / Q000378:metabolism; D007700:Kinetics; D008297:Male; D012756:Sheep / Q000254:growth & development*; D012964:Sodium / Q000378:metabolism*
D012964:Sodium; D005947:Glucose