Specificity of glucose transport inhibitors in the frog lens

Lucas, Valerie A.; Duncan, G.

doi:10.1016/0014-4835(83)90076-3

Cited by 5 publications

(2 citation statements)

References 19 publications

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“…It also was sensitive to phloretin, cytochalasin B, and phlorizin inhibition ( Table 3). As expected, cytochalasin B, which is the more potent inhibitor, showed greater inhibition of facilitative glucose transport than phloretin, as is the cases for bovine RPE (63) and frog lens (40). Since phloretin and cytochalasin B are potent inhibitors of GLUT-type transporters (38 -40), we may conclude that passive facilitated transport is the major mode of glucose transport across the bovine CBE.…”

Section: Discussionmentioning

confidence: 62%

Is active glucose transport present in bovine ciliary body epithelium?

Chan

Guggenheim

2007

American Journal of Physiology-Cell Physiology

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Hyperglycemia is a major risk factor for diabetic cataract formation. Effective regulation of glucose transport by the ciliary body epithelium (CBE) is pivotal to normal glycemic control in the anterior eye, which in turn affects the glucose level of the crystalline lens. The present study aimed to characterize the glucose transport mechanisms across the bovine blood-aqueous barrier (BAB) represented by the CBE. With an Ussing-type chamber, the glucose transport kinetics were measured and characterized in the presence and absence of various glucose transporter inhibitors. The saturation characteristics of the CBE to glucose were estimated from an Eadie-Hofstee plot. The mRNA expression of glucose transporters in specific regions of the bovine CBE was assessed using RT-PCR. The trans-CBE glucose flux was found to be sensitive to the glucose transporter inhibitors cytochalasin B, phloretin, and phlorizin. The transport system had a kinetic constant of 5.3 mM and a maximum velocity of 349.5 nmol.h(-1).cm(-2). Gene expression for GLUT1, GLUT3, GLUT4, GLUT5, and SGLT2 was observed in both the pars plana and pars plicata regions of the bovine CBE. This study demonstrates that glucose transport across the bovine CBE is primarily passive in nature. However, the novel findings of 1) the presence of a phlorizin-sensitive glucose flux and 2) gene expression for SGLT2 mean that a potential role for active glucose transport cannot be ruled out. The elucidation of the exact function of SGLT2 in the bovine CBE may shed important light on the glucose transport and physiology of the BAB and inform future studies of glycemic control in relation to diabetic cataract formation.

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Section: Discussionmentioning

confidence: 62%

Is active glucose transport present in bovine ciliary body epithelium?

Chan

Guggenheim

2007

American Journal of Physiology-Cell Physiology

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“…It could be objected that these measurements do not take into account the known hetero geneity of metabolic events in distinct parts of the lens [25-27], However, a number of prior reports support the concept that the intracellular concentration of D-glucose in the lens is extremely low, at least as long as the extracellular concentration of the hexose does not exceed 7-10 mM [28. 29], Inciden tally, even in the case of the nonmetabolized sugar 3-O-methyl-D-glucose, it takes at least 10 h for the intracellular hexose concentration to reach a steady-state value [30,31].…”

Section: Metabolism Ofd-glucose At Anomeric Equilibriummentioning

confidence: 99%

Metabolism of D-Glucose Anomers in Rat Lens

Sterling¹,

Sener²,

Malaisse³

1988

Ophthalmic Res

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In lens homogenates, hexokinase displayed a greater affinity for α-D-glucose but a higher maximal velocity with β-D-glucose. However, in intact lenses incubated at 10 ^¤ C in the presence of 4–7 mM α- or β-D-glucose, no anomeric difference could be found in either the intracellular content in D-glucose and D-glucose 6-phosphate or the utilization of D-[5–³H]glucose and oxidation of D-[1-¹⁴C]glucose. Even the sorbitol content of the lens was not significantly different after 180 min perifusion at 37 °C in the presence of either α- or β-D-glucose. It is proposed that the lack of anomeric specificity in D-glucose metabolism is attributable, at least in part, to the low turnover rate of glucose 6-phosphate in the lens, allowing for the interconversion of glucose 6-phosphate anomers.

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