This study investigates the presence, localization, and developmental
expression of a neuron-specific facilitated-diffusion glucose transpor
ter, GLUT3, in the rat retina so as to elucidate molecular mechanisms
regulating glucose homeostasis in support of the visual function. Immu
noblot analysis using anti-GLUT3 antibody (ALM3-C) revealed the presen
ce of GLUT3 as a heterogeneously glycosylated protein with an average
molecular weight of approximately 44 kDa. Although immunofluorescence
staining showed it to be localized primarily in the inner and outer pl
exiform layers, some of the cell bodies in the inner nuclear layer als
o showed weak immunoreactivity. Immunoblot analysis of developing rat
retinal tissues revealed the presence of the GLUT3 protein as early as
embryonic day 15 (E15), and immunofluorescence staining revealed its
expression in the inner plexiform layer near the time of birth and in
the outer plexiform layer at postnatal day 14 (P14), i.e., when the ey
es normally open and retinal activity commences. The protein's abundan
ce remained at a relatively low level during the embryonic stages and
up until the end of the first postnatal week (P7), though a transient
increase was confirmed to occur at E18. From P13, however, the abundan
ce steadily increased, rapidly reaching the adult level at P24. Based
on these observations, we hypothesize that GLUT3 is expressed in some
subsets of retinal neurons, being preferentially abundant in their neu
ronal processes, and that its ontogeny is closely associated with morp
hological and functional development of the retina. As such, this sugg
ests that GLUT3 plays some important role(s) in the retina where gluco
se metabolism is essential.