Abstract
ABSTRACTGlucose is transported in crustacean hepatopancreas and intestine by Na+-dependent co-transport, while Na+-dependent D-fructose influx has only been described for the hepatopancreas. It is still unclear if the two sugars are independently transported by two distinct cation-dependent co-transporter carrier systems. In this study, lobster (Homarus americanus) hepatopancreas brush border membrane vesicles (BBMV) were used to characterize, in detail, the cation-dependency of both D-[3H]-glucose and D-[3H]-fructose influxes, while in vitro perfused intestines were employed to determine the nature of cation-dependent sugar transport across this organ. Over the sodium concentration range of 0–100 mM, both [3H]-glucose and [3H]-fructose influxes (0.1 mM; 1 min uptakes) by hepatopancreatic BBMV were hyperbolic functions of [Na+]. [3H]-glucose and [3H]-fructose influxes by hepatopancreatic BBMV over a potassium concentration range of 15–100 mM were hyperbolic functions of [K+]. Both sugars displayed significant (p<0.01) Na+/K+-dependent and cation-independent uptake processes. Transepithelial 25 µM [3H]-glucose and [3H]-fructose fluxes across lobster intestine over luminal sodium and potassium concentration ranges of 0–50 mM and 5–100 mM, respectively, were hyperbolic functions of luminal [Na+] and [K+]. As with hepatopancreatic sugar transport, transepithelial intestinal sugar transport exhibited both significant (p<0.01) Na+/K+-dependent and cation-independent processes. Results suggest that both D-glucose and D-fructose are transported by a single SGLT-type carrier in each organ with sodium being the “preferred”, high affinity, cation for both sugars in the hepatopancreas, and potassium being the “preferred”, high affinity, cation for both sugars in the intestine.
Highlights
Hepatopancreas Effect of freezing on the sugar transport activity of lobster hepatopancreatic BBMV To assess the effect of freezing on the transport activity of lobster hepatopancreatic brush border membrane vesicles (BBMV), vesicles prepared from an individual lobster hepatopancreas were loaded with 300 mM mannitol, 12 mM Hepes/Tris at pH 7.0
The results of the present investigation suggest that both Dglucose and D-fructose are transported across the intestinal epithelium and hepatopancreatic brush border membrane of the American lobster (Homarus americanus), at least in part, by a shared Na+/K+-stimulated transport process with properties resembling those of a mammalian SGLT-type sugar carrier
The present research has examined the effects of a freezing preservation technique on lobster hepatopancreatic BBMV glucose transport characteristics
Summary
The SLC5 co-transporter gene family is a large family of 75 kDa proteins consisting of several sodium-dependent glucose cotransporter proteins (e.g. SGLT) that transport glucose and other solutes such as galactose across biological membranes in conjunction with the cations Na+ or H+ using transmembrane ion Department of Biology, University of North Florida, Jacksonville, FL 32224, USA. Within the last 10 years, a cDNA clone of SGLT4 was isolated from a human small intestine cDNA library and was reported to act as a mannose/1,5anhydro-D-glucitol/fructose (Man/1,5AG/Fru) transporter in the intestine and kidney (Tazawa et al, 2005)
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