Specificity of d-glucose transport by the apical membrane of Nereis diversicolor epidermis |
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Authors: | Sten Albrechtsen Jørgen Gomme |
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Institution: | August Krogh Institute, Zoophysiological Laboratory A, University of Copenhagen, 13 Universitetsparken, DK-2100 Copenhagen Ø Denmark |
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Abstract: | (1) The specificity of d-6-3H]glucose influx by a Na+-dependent and phlorizin-sensitive transport system in the apical epidermal membrane of the polychaete worm, Nereis diversicolor, was investigated in vivo. (2) The inhibitory effect of eleven d-glucose analogues on d-6-3H]glucose influx from a 5 μM external concentration was recorded. The inhibitors (each tested at 5, 50, 500 and 5000 μM) were selected to illuminate the configurational requirements for interaction with the d-glucose transport system. (3) The following compounds were found to be significant inhibitors: methyl α-d-glucoside, methyl β-d-glucoside, d-galactose, , 2-deoxy-d-glucose, d-xylose, myo-inositol, β-d-fructose; the effect was graded according to inhibitor concentration. l-Glucose also inhibited d-glucose influx but to the same extent at all four concentrations tested, suggesting transport site heterogeneity. d-Mannose and l-arabinose did not inhibit influx. (4) The most potent inhibitor, methyl-α-d-glucoside, was itself a substrate, and its transport was inhibited by phlorizin and d-glucose, as well as by substitution of Na+ in the incubation medium with Li+ or choline+. (5) We conclude that the specificity of the Na+-dependent d-glucose transporter in the apical epidermal membrane of Nereis is similar to that in the apical membrane of vertebrate small intestinal and proximal tubular epithelium, and in the tapeworm integument. |
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Keywords: | Glucose analog (N diversicolor epidermis) 65% ASW artificial sea water diluted to 65% of the salinity of ocean water [1] |
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