Submitted on February 2, 2006
Accepted on October 2, 2006
Active glucose transport is present in the bovine ciliary body epithelium (CBE)
Chu Yan Chan1, Jeremy A Guggenheim2, and Chi Ho To3*
1 School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
2 School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom
3 School of Optometry, The Hong Kong Polytechnic University, Hong Kong
* To whom correspondence should be addressed. E-mail: sochto{at}polyu.edu.hk.
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. This study aimed to characterize the glucose transport across the bovine blood-aqueous-barrier (BAB) at the CBE. With an Ussing-type chamber, the glucose transport kinetics were studied in the presence and absence of various glucose transporter inhibitors. The saturation characteristics of the CBE to glucose were estimated by 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 sensitive to the glucose transporter inhibitors cytochalasin B, phloretin and phlorizin. It gave a kinetic constant (Km) of 5.3 mM and a maximum velocity (Vmax) of 349.5 nmolh-1cm-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, indicates a potential role for active glucose transport. The elucidation of the function of SGLT2 in the bovine CBE may shed new light on the glucose homeostasis in the anterior eye.
