title: Kinetics of glucose transport by the perfused mid-gut of the freshwater prawn Macrobrachium rosenberg ii.
abstract: 1. Mucosal influx of [3H]glucose was examined in the mid-gut of a freshwater prawn, Macrobrachium rosenbergii, using an in vitro perfusion technique. 2. [3H]glucose transfer across the apical cell membrane of the epithelium exhibited Michaelis-Menten kinetics (Jmax.in = 0-15 mumole glucose  equiv/g. min, Kt = 0-17 mM). Under Na-free conditions, glucose influx was significantly reduced and a linear function of substrate concentration, indicative of either slow cellular diffusion (KD = 7-6 X 10(3) mumole glucose equiv/g. min. mM) or a facilitated process with a low carrier affinity for the sugar. 3. Phlorizin was a potent competitive inhibitor of glucose influx (K1 = 3-6 X10(-3) mM), galactose and 3-O-methylglucose (3-O-MG) were weak inhibitors, and fructose had no evident effect on glucose uptake. Azide, but not iodoacetate (IAA), significantly depressed influx. 4. Absorbed [3H]glucose was rapidly metabolized by the mid-gut. The majority of accumulated activity within the tissue was in the form of phosphorylated compounds and tritiated water (THO), while only 0-3% was recovered as a free-glucose. 5. Preliminary studies examining transmural [3-H]glucose transport, however, demonstrated a significant net mucosal to serosal free-glucose flux across the prawn mid-gut which was Na-dependent and IAA- and phlorizin-sensitive. Two alternative interpretations of the data are advanced as possible mechanisms for transepithelial glucose transport: (1) group translocation, or (2) the operation of an energized, high affinity, baso-lateral sugar transport carrier.
mesh_terms: D000818:Animals; D001386:Azides / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D004848:Epithelium / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D006601:Hexoses / Q000494:pharmacology; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000378:metabolism*; D007461:Iodoacetates / Q000494:pharmacology; D007700:Kinetics; D033541:Palaemonidae / Q000378:metabolism*; D010695:Phlorhizin / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
chemical_list: D001386:Azides; D006601:Hexoses; D007461:Iodoacetates; D012964:Sodium; D010695:Phlorhizin; D005947:Glucose