title: K⁺-dependent ³H-D-glucose transport by hepatopancreatic brush border membrane vesicles of a marine shrimp.
abstract: The effects of sodium, potassium, sugar inhibitors, and membrane potential on ³H-D-glucose uptake by hepatopancreatic epithelial brush border membrane vesicles (BBMV) of the Atlantic marine shrimp, Litopenaeus setiferus, were investigated. Brush border membrane vesicles were prepared using a MgCl₂/EGTA precipitation method and uptake experiments were conducted using a high speed filtration technique. ³H-D-Glucose uptake was stimulated by both sodium and potassium and these transport rates were almost doubled in the presence of an inside-negative-induced membrane potential. Kinetics of ³H-D-glucose influx were hyperbolic functions of both external Na⁺ or K⁺, and an induced membrane potential increased influx J(max) and lowered K(m) in both salts. ³H-D-Glucose influx versus [glucose] in both Na⁺ or K⁺ media also displayed Michaelis-Menten properties that were only slightly affected by induced membrane potential. Phloridzin was a poor inhibitor of 0.5 mM ³H-D-glucose influx, requiring at least 5 mM in NaCl and 10 mM in KCl to significantly reduce hexose transport. Several sugars (D-galactose, α-methyl-D-gluco-pyranoside, unlabeled D-glucose, D-fructose, and D-mannose) were used at 75 mM as potential inhibitors of 0.1 mM ³H-D-glucose influx. Only unlabeled D-glucose, D-fructose, and D-mannose significantly (p < 0.05) reduced labeled glucose transport. An additional experiment using increasing concentrations of D-mannose (0, 10, 25, 75, and 100 mM) showed this hexose to be an effective inhibitor of 0.1 mM ³H-D-glucose uptake at concentrations of 75 mM and higher. As a whole these results suggest that ³H-D-glucose transport by hepatopancreatic BBMV occurs by a carrier system that is able to use both Na⁺ and K⁺ as drivers, is enhanced by membrane potential, is relatively refractory to phloridzin, and is only inhibited by itself, D-fructose, and D-mannose. These properties are similar to those exhibited by the mammalian SLC5A9/SGLT4 transporter, suggesting that an invertebrate analogue of this protein may occur in shrimp.
authors: Department of Biology, University of North Florida, Jacksonville, FL 32224, USA.
authors: Ijeoma E
authors: IE
authors: Obi
authors: Kenneth M
authors: KM
authors: Sterling
authors: Gregory A
authors: GA
authors: Ahearn
mesh_terms: D000818:Animals; D060829:Arthropod Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001267:Atlantic Ocean; D001692:Biological Transport / Q000187:drug effects; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005431:Florida; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000037:antagonists & inhibitors / Q000378:metabolism; D043143:Hepatopancreas / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008358:Mannose / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D049990:Membrane Transport Modulators / Q000494:pharmacology; D008871:Microvilli / Q000378:metabolism; D033561:Penaeidae / Q000378:metabolism*; D010695:Phlorhizin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D051247:Sodium-Glucose Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014316:Tritium
chemical_list: D060829:Arthropod Proteins; D049990:Membrane Transport Modulators; D051247:Sodium-Glucose Transport Proteins; D014316:Tritium; D005632:Fructose; D012964:Sodium; D010695:Phlorhizin; D005947:Glucose; D008358:Mannose; D011188:Potassium