R. Kannan et al., MOLECULAR CHARACTERIZATION OF A REDUCED GLUTATHIONE TRANSPORTER IN THE LENS, Investigative ophthalmology & visual science, 36(9), 1995, pp. 1785-1792
Purpose. To characterize glutathione (GSH) transporter in the lens. Me
thods. Poly (A)(+)RNA isolated from bovine lens was injected into Xeno
pus laevis oocytes. Oocytes were incubated for 1 hour in either NaCl o
r sucrose medium containing tracer GSH, and cell-associated radioactiv
ity was determined. Glutathione efflux was determined in lens mRNA inj
ected oocytes preloaded with GSH. Relationship of lens GSH transporter
to the two recently cloned sodium-independent hepatic membrane GSH tr
ansporters was studied by Northern blot and reverse transcription-poly
merase chain reaction (RT-PCR) analyses. Bovine lens mRNA also was pro
bed for gamma glutamyl transpeptidase (GGT) by RT-PCR. Results. Uptake
of tracer S-35-GSH could be demonstrated in X. laevis oocytes injecte
d with poly (A)(+)RNA from bovine lens. Glutathione transport was carr
ier mediated (K-m similar to 1.3 mM) and was sodium independent. High-
performance liquid chromatography confirmed that the molecular form of
uptake was predominantly (>98%) as it was for GSH. Poly (A)(+)RNA-inj
ected oocytes preloaded with 16.5 nmol GSH-oocyte showed GSH efflux at
a rate of 2.6 nmol/oocyte per hour. When bovine lens poly (A)(+)RNA w
as hybridized with the cDNA probe for the sodium-independent rat canal
icular GSH transporter (RcGshT), the transcript for RcGshT was observe
d. RT-PCR confirmed the presence of RcGshT and showed the absence of r
at sinusoidal GSH transporter (RcGshT) and GGT mRNA in rat lens. Concl
usions. The authors have demonstrated for the first time that lens con
tains mRNA for RcGshT and expresses a low-affinity GSH transporter in
oocytes. Glutathione efflux from the apical side of the anterior epith
elium and progressive uptake, and inward efflux into cortical fibers,
might be explained by expression of RcGshT alone or in combination wit
h as yet unidentified GSH transporters.