title: Apical sodium-glucose co-transport can be regulated by blood-borne glucose in the ruminal epithelium of sheep (Ovis aries, Merino breed).
abstract: The intestinal Na-dependent D-glucose co-transporter (SGLT)-1 in sheep is under dietary regulation by luminal substrates. The aim of the present study was to find out whether the SGLT-1 in the forestomach of sheep is also regulated by sugars. Furthermore, the location of a possible glucosensor (luminal v. intracellular v. basolateral) was to be elucidated. Ruminal epithelia of sheep (Ovis aries, Merino breed) were pre-incubated in Ussing chambers with various substrates on the mucosal (i.e. luminal) or serosal (i.e. blood) side. This pre-incubation period was followed by a second pre-incubation period without the tested substrates (washout period). Thereafter, apical D-glucose uptake by ruminal epithelial cells was determined with 200 mumol D-[(14)C]glucose/l in the absence or co-presence of the SGLT-1 inhibitor, phlorizin. Pre-incubation with D-glucose on the mucosal side had no significant effect on apical D-glucose uptake (P>0.05). In contrast, pre-incubation with D-glucose, D-mannose, 3-O-methyl-d-glucose or sucrose on the serosal side significantly increased D-glucose uptake compared with mannitol-treated controls (P<0.05). Serosal pre-incubation with cellobiose or D-xylose had no effect. The stimulation of d-glucose uptake by serosal D-glucose pre-incubation was concentration dependent, with maximal stimulation at about 10 mmol/l. We conclude that the ruminal SGLT-1 can be up-regulated in a concentration-dependent manner by blood-borne D-glucose via an extracellular sugar-sensing mechanism.
authors.affiliation: Institute of Veterinary Physiology, Leipzig University, D-04103 Leipzig, Germany.
authors.forename: Cengiz
authors.initials: C
authors.lastname: Atasoglu
authors.forename: Gotthold
authors.initials: G
authors.lastname: Gäbel
authors.forename: Jörg R
authors.initials: JR
authors.lastname: Aschenbach
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D012417:Rumen / Q000378:metabolism*; D012756:Sheep; D012964:Sodium / Q000378:metabolism*; D051269:Sodium-Glucose Transporter 1
chemical_list: D001786:Blood Glucose; D006601:Hexoses; D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D051269:Sodium-Glucose Transporter 1; D012964:Sodium; D005947:Glucose