Department of Biology, University of North Florida, Jacksonville, FL 32224, USA.
Department of Biology, University of North Florida, Jacksonville, FL 32224, USA
Biol Open. 2014 Jun 20;3(7):635-43. doi: 10.1242/bio.20148904.
Glucose 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-[(3)H]-glucose and D-[(3)H]-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 [(3)H]-glucose and [(3)H]-fructose influxes (0.1 mM; 1 min uptakes) by hepatopancreatic BBMV were hyperbolic functions of [Na(+)]. [(3)H]-glucose and [(3)H]-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 [(3)H]-glucose and [(3)H]-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.
葡萄糖在甲壳类动物的肝胰腺和肠道中通过 Na(+)-依赖性共转运进行运输，而 Na(+)-依赖性 D-果糖内流仅在肝胰腺中被描述过。目前尚不清楚这两种糖是否通过两种不同的阳离子依赖性共转运载体系统独立运输。在这项研究中，我们使用龙虾（Homarus americanus）肝胰腺刷状缘膜囊泡（BBMV）来详细描述 D-[(3)H]-葡萄糖和 D-[(3)H]-果糖内流的阳离子依赖性，同时使用体外灌注的肠来确定这种器官中阳离子依赖性糖转运的性质。在 0-100 mM 的钠离子浓度范围内，肝胰腺 BBMV 对 0.1 mM [(3)H]-葡萄糖和 [(3)H]-果糖（1 分钟摄取量）的摄取呈[Na(+)]的双曲线函数。肝胰腺 BBMV 在 15-100 mM 的钾离子浓度范围内对 [(3)H]-葡萄糖和 [(3)H]-果糖的摄取呈[K(+)]的双曲线函数。这两种糖都显示出显著的（p<0.01）Na(+)/K(+)-依赖性和阳离子非依赖性摄取过程。跨龙虾肠上皮的 25 µM [(3)H]-葡萄糖和 [(3)H]-果糖通量，在腔侧钠离子和钾离子浓度范围分别为 0-50 mM 和 5-100 mM 时，均为腔侧[Na(+)]和[K(+)]的双曲线函数。与肝胰腺的糖转运一样，跨肠上皮的糖转运也表现出显著的（p<0.01）Na(+)/K(+)-依赖性和阳离子非依赖性过程。结果表明，D-葡萄糖和 D-果糖都由每个器官中的单个 SGLT 型载体运输，在肝胰腺中，钠离子是两种糖的“首选”、高亲和力阳离子，而在肠道中，钾离子是两种糖的“首选”、高亲和力阳离子。
