scholarly journals The diffusive component of intestinal glucose absorption is mediated by the glucose-induced recruitment of GLUT2 to the brush-border membrane

2000 ◽  
Vol 350 (1) ◽  
pp. 155-162 ◽  
Author(s):  
George L. KELLETT ◽  
Philip A. HELLIWELL
Keyword(s):  
Brush Border ◽  
Glucose Concentration ◽  
Brush Border Membrane ◽  
Glucose Absorption ◽  
Facilitated Diffusion ◽  
Simple Diffusion ◽  
Saturation Kinetics ◽  
Intestinal Glucose Absorption ◽  
Diffusive Component

We have investigated the mechanism responsible for the diffusive component of intestinal glucose absorption, the major route by which glucose is absorbed. In perfused rat jejunum in vivo, absorption was strongly inhibited by phloretin, an inhibitor of GLUT2. The GLUT2 level at the brush-border membrane increased some 2-fold when the luminal glucose concentration was changed from 0 to 100mM. The phloretin-sensitive or diffusive component of absorption appeared superficially linear and consistent with simple diffusion, but was in fact carrier-mediated and co-operative (n = 1.6, [G1/2] = 56mM; where [G1/2] is the glucose concentration at half Vmax) because of the glucose-induced activation and recruitment of GLUT2 to the brush-border membrane. Diffusive transport by paracellular flow was negligible. The phloretin-insensitive, SGLT1-mediated, component of glucose absorption showed simple saturation kinetics with [G1/2] = 27mM: the activation of protein kinase C (PKC) βII, the isoenzyme of PKC that most probably controls GLUT2 trafficking [Helliwell, Richardson, Affleck and Kellett (2000) Biochem. J. 350, 149–154], also showed simple saturation kinetics, with [G1/2] = 21mM. We conclude that the principal route for glucose absorption is by GLUT2-mediated facilitated diffusion across the brush-border membrane, which is up to 3-fold greater than that by SGLT1; the magnitude of the diffusive component at any given glucose concentration correlates with the SGLT1-dependent activation of PKC βII. The implications of these findings for the assimilation of sugars immediately after a meal are discussed.

Potential differences influence amino acid/Na+ symport rates in larval Manduca sexta midgut brush-border membrane vesicles.

1994 ◽  
Vol 189 (1) ◽  
pp. 55-67
Author(s):  
R Parthasarathy ◽  
W R Harvey
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Manduca Sexta ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Rate Determining Step ◽  
Half Saturation Constant

The time-dependent fluorescence intensity of an intravesicular potential-sensitive dye was used to probe the real-time kinetics of potential difference (PD)-dependent amino acid/Na+ symport at pH9 into brush-border membrane vesicles obtained from larval Manduca sexta midgut. Neutral amino acids (alanine, proline) are symported at higher rates as the vesicles are hyperpolarized. The symport rates of acidic (glutamate) and basic (arginine) amino acids are almost PD-independent. The half-saturation constant of alanine is PD-independent between -108 and -78 mV, although the maximal symport velocity increases by half as the voltage is increased. Amino acid throughput is evidently enhanced as the relatively high transmembrane PDs (> 150 mV, lumen positive) measured in vivo are approached. The half-saturation concentrations of Na+ were in the range 15-40 mmol l-1 for most of the amino acids examined and increased with voltage for alanine. The Vmax observed as a function of cation or amino acid concentration increased as the vesicle was hyperpolarized in the case of leucine and alanine. The data support the hypothesis that carrier and substrates are at equilibrium inasmuch as substrate translocation seems to be the rate-determining step of symport.

Mechanism of maleic acid-induced glucosuria in dog kidney

1976 ◽  
Vol 231 (4) ◽  
pp. 1024-1032 ◽  
Author(s):  
M Silverman ◽  
L Huang
Keyword(s):  
Brush Border ◽  
Maleic Acid ◽  
Brush Border Membrane ◽  
Multiple Indicator Dilution ◽  
Dog Kidney ◽  
Proximal Tubular ◽  
Multiple Indicator ◽  
Prior Administration

The multiple indicator-dilution technique in vivo and isolated brush-border membranes in vitro have been used to explore the mechanism of maleic acid-induced glucosuria in dog kidney. The interaction of D-glucose with the antiluminal membrane from the peritubular fluid surface is unaltered. It is demonstrated that alpha-methyl-D-glucoside (alpha MG) enters and exits from the proximal tubular cell only across the brush-border membrane. Then using alphaMG as a reference indicator, it is shown that maleic acid does not cause complete inhibition of D-glucose interaction with the antiluminal membrane from the cytoplasmic surface. The binding of [3H]phlorizin both in vivo and in vitro is not affected by prior administration of maleic acid, indicating that D-glucose interaction with the outside surface of the brush border is also not affected by maleic acid. The data are therefore consistent with the concept that maleic acid-induced glucosuria is due either to i) partial inhibition of D-glucose movement from cytoplasm across the antiluminal membrane into the blood, ii) stimulated movement back across the brush-border membrane into urine, or iii) a combination of the two effects.

Internalization and intracellular transport of folate-binding protein in rat kidney proximal tubule

1993 ◽  
Vol 264 (2) ◽  
pp. C302-C310 ◽  
Author(s):  
H. Birn ◽  
J. Selhub ◽  
E. I. Christensen
Keyword(s):  
Plasma Membrane ◽  
Proximal Tubule ◽  
Brush Border ◽  
Intracellular Transport ◽  
Brush Border Membrane ◽  
Specific Binding ◽  
Binding Protein ◽  
Rat Kidney ◽  
Folate Binding Protein

Folate-binding protein (FBP) is involved in folate reabsorption in the renal proximal tubule. Immunocytochemical studies have located FBP to the brush-border membrane, endocytic vacuoles, and dense apical tubules. We applied the same polyclonal antibody (anti-FBP) against FBP to investigate the dynamic relationship between FBP in the different compartments by microinjecting the antibody into rat kidney proximal tubules in situ. Specific binding of anti-FBP in vivo to the brush-border membrane was followed by fixation at various times. Protein A-gold labeling shows that anti-FBP is transported from endocytic invaginations into vacuoles followed by transport into dense apical tubules within 15 s. Thus FBP is rapidly internalized, and together with previous studies this study strongly suggests recycling of FBP back to the luminal plasma membrane through dense apical tubules. The results are consistent with reabsorption of folate through endocytosis of the FBP-folate complex followed by dissociation and recycling of FBP. When time is allowed there is a steady accumulation of FBP in dense apical tubules combined with an increase in surface density of the same compartment. A possible explanation involves partial inhibition of the fusion between dense apical tubules and plasma membrane because of the anti-FBP labeling of the receptor.

scholarly journals Inhibition of α-Glucosidase, Intestinal Glucose Absorption, and Antidiabetic Properties by Caralluma europaea

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Hayat Ouassou ◽  
Touda Zahidi ◽  
Saliha Bouknana ◽  
Mohamed Bouhrim ◽  
Hassane Mekhfi ◽  
...  
Keyword(s):  
Ethyl Acetate Fraction ◽  
Inhibitory Effect ◽  
Tolerance Test ◽  
Glucose Absorption ◽  
Significant Inhibition ◽  
Oral Glucose ◽  
Glucosidase Activity ◽  
Intestinal Glucose Absorption

Many medicinal plants around the world are used for therapeutic purposes against several diseases, including diabetes mellitus. Due to their composition of natural substances that are effective and do not represent side effects for users, unlike synthetic drugs, in this study, we investigated the inhibitory effect of Caralluma europaea (CE) on α-glucosidase activity in vitro; then the kinetics of the enzyme were studied with increasing concentrations of sucrose in order to determine the inhibition type of the enzyme. In addition, this effect of Caralluma europaea (CE) was confirmed in vivo using rats as an experimental animal model. Among the five fractions of CE, only the ethyl acetate fraction of C. europaea (EACe) induced a significant inhibition of α-glucosidase and its inhibition mode was competitive. The in vivo studies were conducted on mice and rats using glucose and sucrose as a substrate, respectively, to determine the oral glucose tolerance test (OGTT). The results obtained showed that the EACe and the aqueous extract of C. europaea (AECe) have significantly reduced the postprandial hyperglycemia after sucrose and glucose loading in normal and diabetic rats. AECe, also, significantly decreased intestinal glucose absorption, in situ. The results obtained showed that Caralluma europaea has a significant antihyperglycemic activity, which could be due to the inhibition of α-glucosidase activity and enteric absorption of glucose.

Indirect coupling of urate and p-aminohippurate transport to sodium in human brush-border membrane vesicles

1996 ◽  
Vol 270 (1) ◽  
pp. F61-F68 ◽  
Author(s):  
F. Roch-Ramel ◽  
B. Guisan ◽  
L. Schild
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Indirect Coupling ◽  
Sodium Gradient ◽  
Beta Hydroxybutyrate ◽  
Sodium Cotransport ◽  
Stimulation Of

[14C]urate and p-[14C]aminohippurate (PAH) uptake by human brush-border membrane vesicles (BBMV) were measured in the presence of an inwardly oriented sodium gradient. No direct sodium cotransport was observed. Indirect [14C]urate coupling to sodium transport was demonstrated by cis-stimulation of [14C]urate with nicotinate or pyrazinoate (PZA) in the extravesicular medium but not by adding lactate, alpha-ketoglutarate, or beta-hydroxybutyrate. Indirect sodium coupling of [14C]PAH uptake was observed only when alpha-ketoglutarate was added to the extravesicular medium, a mechanism similar to that of basolateral membranes. The ability for PZA (and nicotinate) to cis-stimulate urate uptake was correlated with a high apparent affinity for the urate/anion exchanger. In urate-loaded vesicles, for identical medium concentrations, [14C]PZA uptake via the urateanion exchanger was 10 times higher than [14C]lactate uptake. Such high PZA affinity for the urate exchanger, working in parallel with PZA sodium cotransport can account for the stimulation of urate reabsorption by PZA in vivo.

Facilitated diffusion of urate in avian brush-border membrane vesicles

2002 ◽  
Vol 283 (4) ◽  
pp. C1155-C1162 ◽  
Author(s):  
Steven M. Grassl
Keyword(s):  
Membrane Potential ◽  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Facilitated Diffusion ◽  
Transport Pathways ◽  
Proximal Tubule Cells ◽  
Avian Kidney

Membrane transport pathways mediating transcellular secretion of urate across the proximal tubule were investigated in brush-border membrane vesicles (BBMV) isolated from avian kidney. An inside-positive K diffusion potential induced a conductive uptake of urate to levels exceeding equilibrium. Protonophore-induced dissipation of membrane potential significantly reduced voltage-driven urate uptake. Conductive uptake of urate was inhibitor sensitive, substrate specific, and a saturable function of urate concentration. Urate uptake was trans-stimulated by urate and cis-inhibited by p-aminohippurate (PAH). Conductive uptake of PAH was cis-inhibited by urate. Urate uptake was unaffected by an outward α-ketoglutarate gradient. In the absence of a membrane potential, urate uptake was similar in the presence and absence of an imposed inside-alkaline pH gradient or an outward Cl gradient. These observations suggest a uniporter-mediated facilitated diffusion of urate as a pathway for passive efflux across the brush border membrane of urate-secreting proximal tubule cells.

Cholera toxin facilitates calcium transport in jejunal brush border vesicles

1986 ◽  
Vol 64 (5) ◽  
pp. 568-574 ◽  
Author(s):  
David D. Maenz ◽  
G. W. Forsyth
Keyword(s):  
Cholera Toxin ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Equilibrium Dialysis ◽  
Membrane Vesicles ◽  
Second Messenger ◽  
Brush Border Membrane Vesicles ◽  
Ionophore A23187

Cholera toxin is very well characterized in terms of the activation of adenylate cyclase. In some systems, however, this cyclase activation does not seem to account for all of the physiological responses to the toxin. On the premise that cholera toxin may also exert effects through other second messenger compounds we have studied the effect of cholera toxin on the rate of Ca2+ movement across the membrane of intestinal brush border vesicles. Increasing concentrations of cholera toxin progressively accelerated the passive uptake of Ca2+ into, and the efflux of Ca2+ from, an osmotically active space in brush border membrane vesicles. This effect of cholera toxin was saturable by excess Ca2+ and was relatively specific, as the toxin did not affect vesicle permeability to an uncharged polar solute. The toxin had two high affinity Ca2+ binding sites on the A subunit as measured by equilibrium dialysis. Ca2+ transport facilitated by cholera toxin was temperature dependent, required the holotoxin, and could be inhibited by preincubation of the toxin with excess free ganglioside GM1.This increased rate of Ca2+ influx caused by the in vitro addition of cholera toxin to brush border membrane vesicles may have physiological significance as it was comparable to rates observed with the Ca ionophore A23187. Similar effects occurring in vivo could permit cholera toxin to increase cytoplasmic Ca2+ concentrations and to produce accompanying second messenger effects.

scholarly journals Renal handling of phosphate in vivo and in vitro by the X-linked hypophosphatemic male mouse: Evidence for a defect in the brush border membrane

1978 ◽  
Vol 14 (3) ◽  
pp. 236-244 ◽  
Author(s):  
Harriet S. Tenenhouse ◽  
Charles R. Scriver ◽  
Roderick McInnes ◽  
Francis H. Glorieux
Keyword(s):  
Brush Border ◽  
Male Mouse ◽  
Brush Border Membrane ◽  
Renal Handling
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