Epithelial glucose transport by lobster antennal gland

Abstract

Transport of d-[3H]glucose into lobster (Homarus americanus)brush-border membrane vesicles (BBMVs) prepared by Mg2+ precipitation from antennal gland labyrinth-coelomosac tissue was examined. Influx of d-glucose occurred primarily by a phlorizin-sensitive, Na+-dependent carrier similar to that found in vertebrate renal epithelium. An inwardly directed Na+ gradient drove concentrative d-glucose uptake, whereas similar gradients of Li+ and K+ did not. Stimulation by the Na+ gradient was further enhanced by the imposition of an inside-negative potential difference and also by increases in the pH of the vesicle and incubation media. An analysis of cis inhibition of d-glucose uptake by a number of sugars and sugar derivatives indicated that the transporter requires (a)that the sugar substrate be a d-pyranose in the C1 chair conformation and(b) that the hydroxyl groups at C2 and C3 of the ring be unmodified and equatorial. Apparent kinetic parameters for glucose uptake were determined under zero-trans, short-circuited conditions. Maximal influx of d-glucose into vesicles was estimated to be 96 pmol mg-1 protein s-1. Half-maximal influx was determined to occur at 0.20 mmol l-1 d-glucose. The relationship between external Na+ concentration and glucose influx was sigmoidal, and the stoichiometry of Na+-dependent glucose transport found to be 3 Na+:1 glucose using the static head method.