Expression of the Na+/glucose co-transporter (SGLT1) in the intestine of domestic and wild ruminants.

The activity and abundance of the Na+/glucose co-transporter (SGLT1) was assessed in brush-border-membrane vesicles (BBMV) isolated from the intestine of grass- and roughage- (GR) consuming ruminants (sheep and dairy cattle), during the transition from the pre-ruminant to the mature ruminant state. The abundance of SGLT1 messenger ribonucleic acid (mRNA) was also compared in the intestinal tissue of the same animals. The dramatic developmental decline in the activity and expression of SGLT1 appears to be typical of GR-consuming ruminants and is coincident with the significant decline in the levels of lumenal monosaccharides. Expression of the ovine SGLT1 complementary deoxyribonucleic acid (cDNA) in Xenopus laevis oocytes confirmed that the isolated cDNA encodes for a functional Na+/glucose co-transporter. Determination of a bovine intestinal SGLT1 protein sequence (amino acids 347-658) indicated 99% similarity to the ovine SGLT1 protein with differences in the carboxyl terminus. In contrast to GR-consuming ruminants, the abundance of SGLT1 protein and SGLT1 mRNA remained significantly high in the intestine of ruminants in both the intermediate-mixed (IM) feeding goat and fallow deer and the concentrate-selecting (CS) moose and roe deer, dietary groups correlating with the availability of monosaccharides in the intestinal lumen.