Biomedical subjects

E Brot-Laroche

Publications and source records attributed to E Brot-Laroche.

7 recordsLinked to original sources

PubMed1992

Fructose transporter in human spermatozoa and small intestine is GLUT5.

We recently reported that the glucose transporter isoform, GLUT5, is expressed on the brush border membrane of human small intestinal enterocytes (Davidson, N. O., Hausman, A. M. L., Ifkovits, C. A., Buse, J. B., Gould, G. W., Burant, C. F., and Bell, G. I. (1992) Am. J. Physiol. 262, C795-C800). To define its role in sugar transport, human GLUT5 was expressed in Xenopus oocytes and its substrate specificity and kinetic properties determined. GLUT5 exhibits selectivity for fructose transport, as determined by inhibition studies, with a Km of 6 mM. In addition, fructose transport by GLUT5 is not inhibited by cytochalasin B, a competitive inhibitor of facilitative glucose transporters. RNA and protein blotting studies showed the presence of high levels of GLUT5 mRNA and protein in human testis and spermatozoa, and immunocytochemical studies localize GLUT5 to the plasma membrane of mature spermatids and spermatozoa. The biochemical properties and tissue distribution of GLUT5 are consistent with a physiological role for this protein as a fructose transporter.

Animals↗

PubMed1992

Expression and localization of GLUT-5 in Caco-2 cells, human small intestine, and colon.

The human colon carcinoma cell line Caco-2 was used as an enterocyte model to study the expression of the facilitative glucose transporters GLUT-1 and GLUT-2, and of the putative hexose transporter GLUT-5, which are expressed specifically in the gut. Northern blots indicate that Caco-2 cells express GLUT-1 and GLUT-5 mRNAs but not the mRNA coding for the basolateral glucose transporter GLUT-2. The level of GLUT-5 mRNA is growth dependent, being detectable only in postconfluent differentiated cells. In addition, the expression of GLUT-5 increases with the number of cell passages and is approximately 10 times higher in later passages (passage 184) than in early ones (passage 26). With the use of polyclonal antibodies directed against the COOH-terminus of GLUT-5, indirect immunofluorescence and Western blotting indicate that GLUT-5 is mainly localized to the brush border of Caco-2 cells. GLUT-5 is also found to be associated with the brush border of epithelial cells from fetal and normal adult human small intestine, but is absent from the colon.

Adult↗

PubMed1989

Fixation of Clostridium difficile toxin A and cholera toxin to intestinal brush border membranes from axenic and conventional mice.

We have tested the in vitro binding of Clostridium difficile toxin A (enterotoxin) and cholera toxin to intestinal brush border membranes prepared from either conventional or axenic mice. Membranes from axenic mice were shown to be saturated at a lower toxin A concentration (at least 2.5 times lower). Because there were no significant differences between membranes from axenic and conventional mice in binding at low toxin A concentrations, the presence of the normal microflora seems to increase the number but not the affinity of brush border membrane receptors on the enterocyte surface. Corroborating the in vitro results, we observed that conventional mice were more sensitive to the pathological effects of toxin A given intragastrically than were axenic mice. In contrast, there was no difference in the binding characteristics of cholera toxin between membranes from conventional and axenic mice. We conclude that the presence of the mouse intestinal bacteria increases the number of C. difficile toxin A intestinal receptors but does not influence cholera toxin receptors.

Animals↗

PubMed1988

Independent modulation by food supply of two distinct sodium-activated D-glucose transport systems in the guinea pig jejunal brush-border membrane.

D-glucose transport across the intestinal brush-border membrane involves two transport systems designated here as systems 1 and 2. Kinetic properties for both D-glucose and methyl alpha-D-glucopyranoside transport were measured at 35 degrees C by using brush-border membrane vesicles prepared from either control, fasted (48 hr), or semistarved (10 days) animals. The results show the following: (i) The sugar influx rate by simple diffusion was identical under either altered condition. (ii) Semistarvation stimulated D-glucose uptake by system 2 (both its Vmax and Km increased), whereas system 1 was untouched. (iii) Fasting increased the capacity of system 1 without affecting either Km of system 1 or Vmax and Km of system 2. The effect of fasting on Vmax of system 1 cannot be attributed to indirect effects from changes in ionic permeability because the kinetic difference between control and fasted animals persisted when the membrane potential was short-circuited with equilibrated K+ and valinomycin. This work provides further evidence for the existence of two distinct sodium-activated D-glucose transport systems in the intestinal brush-border membrane, which adapt independently to either semistarvation or fasting.

Animals↗

PubMed1986

Temperature sensitivity and substrate specificity of two distinct Na+-activated D-glucose transport systems in guinea pig jejunal brush border membrane vesicles.

D-Glucose transport was studied with isolated brush border membrane vesicles from guinea pig jejunum. Saturation curves were carried out at either 25 or 35 degrees C in buffers containing Na+, Li+, K+ (100 mM chloride salt), or sorbitol (200 mM). Uncorrected uptake rates were fitted by nonlinear regression analysis to an equation involving one diffusional and two saturable terms. In the presence of Na+ at 35 degrees C, two saturable systems (Km = 0.4 and 24 mM, respectively) were evident, as well as a diffusion component quantitatively identical with that measured with L-glucose in separate experiments. In contrast, at 25 degrees C only one saturable system was apparent (Km = 1.2 mM): the second exhibited diffusion-like kinetics. In the presence of Na+ at 35 degrees C, D-glucose uptake was fully inhibited by both D-glucose and D-galactose, whereas alpha-methylglucoside gave kinetics of partial inhibition. We conclude that in the presence of Na+ there are at least two distinct D-glucose transport systems: 1) System I, a low temperature-sensitive system, fully inhibited by D-glucose, D-galactose, and alpha-methylglucoside; we identify it as the "classical" D-glucose/Na+ cotransport system, insensitive to inhibition by cytochalasin B and obligatorily dependent on Na+; and 2) System II, a high temperature-sensitive system where D-glucose and D-galactose inhibit but alpha-methylglucoside is inert. Its cation specificity is unclear but it appears to be sensitive to cytochalasin B inhibition. When Li+ or K+ substituted for Na+, only one transport system was apparent. The Li+-activated transport was: independent of the incubation temperature; inhibited by D-glucose and D-galactose but not by alpha-methylglucoside, 2-deoxy-D-glucose, D-mannose, and D-xylose; and sensitive to cytochalasin B inhibition. The exact nature of the system (or systems) involved in D-glucose transport in the absence of sodium remains to be established.

Animals↗

PubMed1979

The effect of harmaline on intestinal sodium transport and on sodium-dependent D-glucose transport in brush-border membrane vesicles from rabbit jejunum.

Harmaline inhibition of sodium uptake and of sodium-dependent D-glucose transport was investigated using brush-border membrane vesicles from frozen rabbit jejunum. Under sodium-gradient conditions, "initial" D-glucose uptake (20 s) was inhibited by harmaline at concentrations above 0.5 mM, but at lower harmaline concentrations D-glucose uptake was stimulated by 10--15%. When a similar potassium gradient was used, harmaline had no effect. At concentrations up to 2 mM, harmaline did not alter the equilibrium uptake of D-glucose or D-mannitol. After pre-equilibration with sodium (25 mM), G-glucose uptake was inhibited at harmaline concentrations ranging from 0.1 to 2 mM. Sodium (10 mM) uptake was also inhibited by harmaline. Increasing the sodium concentration reduced the inhibitory effect of harmaline on tracer sodium uptake as well as on sodium-dependent D-glucose uptake. Similar to phlorizin, harmaline (1 mM) was able to prevent glucose-induced sodium influx across the brush-border membrane. Sodium uptake into brush-border membrane vesicles seems to be inhibited at lower harmaline concentrations than sodium-dependent D-glucose uptake. At high (2 mM) inhibitor concentrations, however, sodium-dependent glucose uptake is more strongly inhibited than sodium uptake. These results suggest that harmaline inhibits both sodium and sodium-dependent transport across intestinal brush-border membranes by interacting with specific sodium-binding sites.

Alkaloids↗

PubMed1979

Biliary cholesterol absorption in normal and L-thyroxin-fed rats.

Infusion of bile containing labeled cholesterol into bile fistula rats has permitted an in vivo study of the movements and of the absorption of biliary cholesterol in the digestive tract. The specific activities of cholesterol were similar in the micelles and the sediment of the luminal content after a 6 hr infusion, indicating rapid exchange of cholesterol between these fractions. In animals fed a basal diet, the biliary cholesterol absorption was higher (83%) than that of dietary cholesterol (70%). Bile cholesterol is essentially absorbed in the jejunum while the absorption of cholesterol from the diet takes place all along the small intestine but preferentially in its second and third quarters. Both alimentary cholesterol and bile cholesterol enter the top cells of the villi in preference to those of the crypts. In L-thyroxin-fed rats, a parallel decrease in biliary and dietary cholesterol absorption was observed. The increase in the intestinal transit of cholesterol and epithelium cell renewal of the jejunum accounted for this observation.

Animals↗