Functional characterization of a novel disaccharide transporter in lobster hepatopancreas.
In animals, the accepted model of carbohydrate digestion and absorption involves reduction of disaccharides into the monosaccharides glucose, fructose, and galactose followed by their individual transmembrane transport into cells. In 2011, a gene for a distinct disaccharide sucrose transporter (SCRT) was found in Drosophila melanogaster and characterized in a yeast expression system. The purpose of the present investigation was to functionally identify and characterize a putative disaccharide transporter analog in the hepatopancreas of the American lobster, Homarus americanus. Purified hepatopancreatic brush-border membrane vesicles (BBMV) were used in transport experiments using14C-sucrose and a Millipore filter isolation technique. In the absence of sodium, an external pH of 4 significantly stimulated the uptake of14C-sucrose compared to that occurring at pH 5, 6, or 7. At pH 7, increasing external concentrations of sodium increased14C-sucrose uptake by BBMV in a hyperbolic fashion and this stimulation was significantly reduced when the pH was changed to 4, suggesting that both protons and sodium ions were each capable of driving the uptake of the sugar. In experiments with a variety of monosaccharides, disaccharides, and trisaccharides, used as potential inhibitors of14C-sucrose uptake, only maltose and trehalose inhibited carrier-mediated14C-sucrose transport. An additional experiment showed that 20 mM maltose was a competitive inhibitor of14C-sucrose uptake. The use of a putative lobster SCRT by both maltose and trehalose is nutritionally appropriate for lobsters as they commonly digest glycogen and chitin, polymers of maltose and trehalose, respectively. These findings suggest there is a brush-border proton- or sodium-dependent, hepatopancreatic carrier process, shared by sucrose, maltose, and trehalose, that may function to absorb disaccharides that are produced from digestion of naturally occurring dietary constituents.
Department of Biology, University of North Florida, Jacksonville, FL, 32223, USA.
Olivia
O
Scheffler
Department of Biology, University of North Florida, Jacksonville, FL, 32223, USA. gahearn@unf.edu.
Gregory A
http://orcid.org/0000-0002-2155-1771
GA
Ahearn
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes / Q000378:metabolism; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D004187:Disaccharides / Q000378:metabolism* / Q000494:pharmacology; D043143:Hepatopancreas / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008320:Maltose / Q000378:metabolism / Q000494:pharmacology; D008871:Microvilli / Q000378:metabolism; D008121:Nephropidae / Q000737:chemistry / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism; D014199:Trehalose / Q000378:metabolism
D002250:Carbon Radioisotopes; D002352:Carrier Proteins; D004187:Disaccharides; D013395:Sucrose; D008320:Maltose; D012964:Sodium; D014199:Trehalose
BBMV; Brush-border membrane; Co-transport; Competitive inhibition; Disaccharides; Hepatopancreas; Homarus americanus; Lobster; Maltose; Proton-dependent; SCRT; Sodium-dependent; Sucrose; Sugar transport; Symport; Trehalose