Functional and molecular biological evidence of SGLT-1 in the ruminal epithelium of sheep.
Because of the effective catabolism of D-glucose to short-chain fatty acids by intraruminal microorganisms, the absorption of D-glucose from the rumen was thought to be of minor importance. However, clinical studies suggested that significant quantities of D-glucose are transported from the ruminal contents to the blood. We therefore tested the ruminal epithelium of sheep for the presence of Na(+)-glucose cotransporter 1 (SGLT-1) on both the functional and mRNA levels. In the absence of an electrochemical gradient, 3-O-methylglucose (3-OMG) was net absorbed across isolated ruminal epithelia mounted in Ussing chambers. The net transport of 3-OMG followed Michaelis-Menten kinetics and was sensitive to phlorizin or decreasing Na(+) concentrations. The mucosal addition of 10 mM D-glucose induced an immediate, phlorizin-sensitive increase in short-circuit current (I(sc)). I(sc) could also be increased by serosal addition of D-glucose or D-mannose, but electrogenic uptake of D-glucose or 3-OMG added on the mucosal side was still detectable after serosal stimulation of I(sc). RT-PCR using primers specific for the ovine intestinal SGLT-1 with subsequent TA cloning and sequencing revealed 100% identity between the cloned cDNA and mRNA fragment 187-621 of ovine intestinal SGLT-1. In conclusion, the ruminal epithelium has a high-affinity SGLT-1, which indicates that it maintains the capacity for D-glucose absorption.
Aschenbach
J R
JR
Veterinär-Physiologisches Institut, Universität Leipzig, Germany.
Wehning
H
H
Kurze
M
M
Schaberg
E
E
Nieper
H
H
Burckhardt
G
G
Gäbel
G
G
D019325:3-O-Methylglucose / Q000493:pharmacokinetics; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D004558:Electric Stimulation; D004847:Epithelial Cells / Q000378:metabolism; D005753:Gastric Mucosa / Q000166:cytology / Q000378:metabolism*; D015870:Gene Expression / Q000502:physiology; D005947:Glucose / Q000493:pharmacokinetics; D008358:Mannose / Q000493:pharmacokinetics; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D012417:Rumen / Q000166:cytology / Q000378:metabolism*; D012756:Sheep; D051269:Sodium-Glucose Transporter 1
D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D051269:Sodium-Glucose Transporter 1; D019325:3-O-Methylglucose; D005947:Glucose; D008358:Mannose