Glucose transport by lobster hepatopancreatic brush-border membrane vesicles

1985 ◽  
Vol 248 (2) ◽  
pp. R133-R141 ◽  
Author(s):  
G. A. Ahearn ◽  
M. L. Grover ◽  
R. E. Dunn
Keyword(s):  
Glucose Uptake ◽  
Glucose Transport ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Apical Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Michaelis Constant ◽  
Diffusional Permeability ◽  
Apparent Diffusion

Epithelial brush-border membrane vesicles (BBMV) were made from lobster hepatopancreas by using Mg2+ precipitation. Alkaline phosphatase, Na+-K+-ATPase, and cytochrome c oxidase activities in these vesicles were enriched 15.0-, 1.0-, and 0.19-fold, respectively, compared with activities of a washed original homogenate pellet, indicating a relatively pure apical membrane preparation reduced in basolateral or organelle contamination. Complete vesicular closure was confirmed with electron microscopy and equilibrium [3H]D-glucose uptake experiments using various transmembrane osmotic gradients. Glucose uptake was stimulated by a transmembrane Na+ gradient but not by an identical K+ gradient or by a Na+ gradient in the presence of phloridzin. Electrogenicity of Na+-dependent glucose transport was confirmed in two ways. First, an anion permeability sequence indicated glucose uptake was stimulated in the following order: SCN- greater than Cl- greater than gluconate- greater than SO4(2-). Second, an outwardly directed valinomycin-induced K+ diffusion potential, rendering the vesicle interior electrically negative, enhanced glucose uptake compared with K+-loaded vesicles lacking the ionophore. Glucose influx occurred by a combination of carrier-mediated transfer, illustrating Michaelis-Menten kinetics, and nonsaturable “apparent diffusion.” pH (same on both sides) strongly influenced Na+-dependent glucose uptake according to the sequence: pH 6.0 greater than pH 7.4 greater than pH 8.0. Increased proton concentration lowered the Michaelis constant for glucose transport and increased the apparent diffusional permeability of the membrane to the sugar. Maximal carrier-mediated glucose transport rate was largely unaffected by pH.(ABSTRACT TRUNCATED AT 250 WORDS)

D-glucose uptake is increased in jejunal brush-border membrane vesicles from hyperthyroid chicks

1989 ◽  
Vol 120 (4) ◽  
pp. 435-441 ◽  
Author(s):  
Hanna Debiec ◽  
Heide S. Cross ◽  
Meinrad Peterlik
Keyword(s):  
Glucose Uptake ◽  
Glucose Transport ◽  
Brush Border ◽  
Transmembrane Potential ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Potential Difference ◽  
Daily Injection ◽  
Transmembrane Potential Difference

Abstract. Jejunal brush-border membrane vesicles were harvested from 4-week old chicks whose thyroid status had been altered either by a daily injection of 20 μg T3 for 1 week or which through the preceding 4 weeks had received propylthiouracil and than had been repleted with either 20 or 80 μg T3 in divided doses within 48 h. T3 markedly stimulated D-glucose uptake in brush-border membrane vesicles in the presence of an outside/inside (100/0 mmol/l) Na+ gradient. T3 administration had no detectable influence on the Na+ permeability of the isolated vesicles. The effect of the thyroid hormone on Na+ gradient-driven D-glucose uptake was fully preserved at zero transmembrane potential difference. These findings exclude that T3 stimulates Na+-dependent D-glucose transport in the small intestine through changes of the electrochemical Na+ gradient or through alteration of the transmembrane potential difference. Tracer exchange experiments under equilibrium and voltageclamp conditions revealed a significantly shorter halftime of D-glucose uptake in brush-border membrane vesicles from T3-treated chicks. Kinetic analysis showed that T3 administration significantly increases the apparent maximal velocity of D-glucose transport in brushborder membrane vesicles, whereas the apparent Km values were virtually unaltered. From these data we conclude that T3 increases the activity of Na+-dependent D-glucose carriers in the brush-border membrane. This is interpreted as consistent with a greater rate of D-glucose absorption from the intestinal lumen under conditions of hyperthyroidism.

Inositol Transport by Hepatopancreatic Brush-Border Membrane Vesicles of the Lobster Homarus Americanus

1988 ◽  
Vol 140 (1) ◽  
pp. 107-121
Author(s):  
TEVA SIU ◽  
GREGORY A. AHEARN
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Homarus Americanus ◽  
Brush Border Membrane Vesicles ◽  
Carrier Mechanism ◽  
Apparent Diffusion ◽  
Noncompetitive Inhibitor ◽  
Inositol Uptake ◽  
Glucose Carrier

The mechanism of [3H]myo-inositol transport by the lobster hepatopancreas was examined using purified brush-border membrane vesicles. Transport was stimulated by a 100 mmoll−1 inward Na+ gradient, but other cation gradients were ineffective, suggesting a Na+-dependent transfer mechanism. The transport system was most efficient at pH7.0 (both sides), rather than in the presence of a pH gradient (pHin = 7.0; pHout = 5.5) or at bilaterally low pH (pHin = pHout = 5.5). The system was shown to be electrogenic in two different ways. First, myo-inositol uptake was stimulated by anions of increasing permeability (SCN− > Cl− > gluconate). Second, an outwardly directed, valinomycin-induced K+ diffusion potential (inside negative) enhanced uptake in comparison with vesicles lacking the ionophore. Myo-inositol was transported by a carrier mechanism with an apparent Kt of 0.79mmoll−1, a Jmax of 6.3pmolmg protein−1 s−1, and by apparent diffusion with a permeability coefficient of 5.92 pmolmg protein−1s−1 (mmolT1)−1. D-Glucose was a noncompetitive inhibitor of myo-inositol uptake, but myo-inositol did not significantly reduce the transport of D-[3H]glucose. Vesicles preloaded with myo-inositol trans-stimulated [3H]myo-inositol uptake, whereas those preloaded with D-glucose did not, suggesting that the inositol carrier did not transport D-glucose. It is proposed that myo-inositol does not share the glucose carrier, and that D-glucose may modulateinositol influx by binding to a ‘regulator’ site on the inositol carrier.

Ionic permeabilities of rat renal cortical brush-border membrane vesicles

1987 ◽  
Vol 252 (4) ◽  
pp. F700-F711
Author(s):  
M. S. Lipkowitz ◽  
R. G. Abramson
Keyword(s):  
Membrane Potential ◽  
Glucose Uptake ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Electrolyte Concentration ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Prolonged Incubation ◽  
New Methods ◽  
Electrochemical Equilibrium

It is generally assumed that electrolytes equilibrate readily across renal cortical brush-border membrane vesicles (BBMV). This assumption was tested by use of two new methods in rat BBMV prepared with free-flow electrophoresis (FFE), Mg aggregation, or Ca aggregation. Intravesicular KCl and RbCl concentrations, as well as the conductance of Cl relative to K (GCl/GK) and GNa/GK were determined with the fluorescent, potential-sensitive probe 3,3'-dipropylthiadicarbocyanine iodide [diS-C3-(5)]; intravesicular KCl concentration was also approximated utilizing the response of Na-dependent [3H]glucose uptake to variations in the membrane potential. These studies demonstrated that KCl fails to attain electrochemical equilibrium in BBMV prepared by the three methods, despite prolonged incubation at 22 degrees C; a significant, inwardly directed electrolyte gradient was sustained in all cases. The intravesicular electrolyte concentration was lower in BBMV prepared with FFE than in those prepared with Mg or Ca. GCl/GK was lowest in BBMV prepared with FFE and highest in those prepared with Ca; GNa/GK was comparable in all preparations. The apparent impermeance of BBMV may impact significantly in interpreting data from studies that require knowledge of the precise concentration of intravesicular electrolytes.

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