Expression and Localization of Carnitine/Organic Cation Transporter OCTN1 and OCTN2 in Ocular Epithelium

¹ Institute for Eye Research, Sydney, New South Wales, Australia; School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia
² Institute for Eye Research, Sydney, New South Wales, Australia
³ Allergan Inc, Lake Forest, California, United States

^* To whom correspondence should be addressed. E-mail: q.garrett{at}ier.org.au.

	Abstract

PURPOSE: Existence of an organic cation transport process in rabbit cornea and conjunctiva that mediates absorption of carnitine has been suggested previously. This study was to determine expression and localization of the carnitine/organic cation transporter (OCTN1 and OCTN2) in corneal or conjunctival epithelium. METHODS: Reverse transcriptase-polymerase chain reaction (RT-PCR) was used for OCTN1 and OCTN2 mRNA expression in the cultured human corneal-limbal epithelial (HCLE) or conjunctival epithelial (HCjE) cells. Immunofluorescence staining using polyclonal antibody against human OCTN1 or OCTN2 was performed to investigate the transporter expression in ocular epithelial cells or rabbit corneal and conjunctival epithelium. The polarity of the transporter expression was determined using western blot analysis of the apical or basal membrane proteins extracted from the cultured cells. Apical or basal uptake of [H3]-L-carnitine was determined using the polarized epithelial cells grown onto collagen-coated porous filter support. RESULTS: OCTN1 and OCTN2 mRNA expression was detected in both HCLE or HCjE cells of rabbits and humans. OCTN1 and OCTN2 were predominately localized in the apical membrane of the cells. Both HCLE and HCjE cells were able to take up L-carnitine, with the majority of carnitine uptake being through the apical surfaces. CONCLUSION: This report is the first to document expression of OCTN1 and OCTN2 in human corneal and conjunctival epithelial cells. These findings suggest a potential involvement of OCTN1 and OCTN2 in transport of carnitine in ocular tissues.

Key Words: dry eye, corneal epithelium, membrane transport

This article has been cited by other articles:

				C. D. Klaassen and L. M. Aleksunes Xenobiotic, Bile Acid, and Cholesterol Transporters: Function and Regulation Pharmacol. Rev., March 1, 2010; 62(1): 1 - 96. [Abstract] [Full Text] [PDF]