Submitted on January 20, 2004
Accepted on September 22, 2004
Expression of monocarboxylate transporters in rat ocular tissues
Glyn Chidlow1*, John P Wood1, Mark Graham2, and Neville N Osborne1
1 Nuffield Laboratory of Ophthalmology, University of Oxford, Oxford, United Kingdom
2 Safety Assessment UK, AstraZeneca, Loughborough, United Kingdom
* To whom correspondence should be addressed. E-mail: glyn.chidlow{at}eye.ox.ac.uk.
The aim of the present study was to determine the distribution of monocarboxylate transporter (MCT) subtypes 1-4 in the various structures of the rat eye using a combination of conventional and real-time RT-PCR, immunoblotting and immunohistochemistry. Retinal samples expressed mRNAs encoding all four MCTs. MCT1 immunoreactivity was observed in photoreceptor inner segments, Muller cells, retinal capillaries and the two plexiform layers. MCT2 labelling was concentrated in the inner and outer plexiform layers. MCT4 immunolabelling was only present in the inner retina, in particular in putative Muller cells, and the plexiform layers. No MCT3 labelling could be observed. The RPE/choroid expressed high levels of MCT1 and 3 mRNAs but lower levels of MCT2 and 4 mRNAs. MCT1 was localised to the apical and MCT3 to the basal membrane of the RPE, while MCT2 staining was faint. Although MCT1-4 mRNAs were all detectable in iris and ciliary body samples, only MCT1 and MCT2 proteins were expressed. These were present in the iris epithelium and the non-pigmented epithelium of the ciliary processes. MCT4 was localised to the smooth muscle lining of large vessels in the iris-ciliary body and choroid. In the cornea, MCT1 and MCT2 mRNAs and proteins were both detectable in the epithelium and endothelium, while evidence was found for the presence of MCT4 and to a lesser extent MCT1 in the lens epithelium. The unique distribution of MCT subtypes in the eye is indicative of the pivotal role that these transporters play in the maintenance of ocular function.
