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 mmol 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.

Effects of dietary menthol-rich bioactive lipid compounds on zootechnical traits, blood variables and gastrointestinal function in growing sheep

“…This is remarkable and supports the functional relevance of a previously postulated sugar-sensing mechanism on the basolateral side of ruminal epithelia. An earlier study had shown that serosal pre-incubation with D -glucose, D -mannose, 3-O-methyl- D -glucose or sucrose can up-regulate apical glucose uptake of isolated ruminal epithelia via such sensor [60]. It was speculated in that previous publication that the functional relevance of this mechanism is to adapt ruminal glucose absorption to the supply of easily fermentable carbohydrates, especially sugars, to the rumen because increased sugar supply to the rumen can effectively trigger an increase in blood glucose [60].…”

“…An earlier study had shown that serosal pre-incubation with D -glucose, D -mannose, 3-O-methyl- D -glucose or sucrose can up-regulate apical glucose uptake of isolated ruminal epithelia via such sensor [60]. It was speculated in that previous publication that the functional relevance of this mechanism is to adapt ruminal glucose absorption to the supply of easily fermentable carbohydrates, especially sugars, to the rumen because increased sugar supply to the rumen can effectively trigger an increase in blood glucose [60]. This is different from the intestine of sheep where upregulation of glucose absorption is also triggered by an increased supply of sugars but the sensor is luminal [61–63].…”

Effects of methionine partially replaced by methionyl‐methionine dipeptide on intestinal function in methionine‐deficient pregnant mice

“…Furthermore, SGLT1 expression was upregulated in the ileum of the Met‐Met group than the Met group, which was consistent with different blood glucose levels in these two groups. It may be resulted from higher blood glucose level in the Met‐Met group via an extracellular sugar‐sensing mechanism (Atasoglu, Gäbel, & Aschenbach, ).…”

Glucose, epithelium, and enteric nervous system: dialogue in the dark

“…Short‐term influences are due to activation or inactivation of transport proteins whereas long‐term influences are due to changes of mRNA‐expression, i.e., by influencing the transcription process. Concerning rapid changes, Atasoglu et al. (2004) have shown that the ovine SGLT1 can be stimulated by glucose and other substrates within minutes.…”