TRANSPORT OF CIRCULATING REDUCED GLUTATHIONE AT THE BASOLATERAL SIDE OF THE ANTERIOR LENS EPITHELIUM - PHYSIOLOGICAL IMPORTANCE AND MANIPULATIONS

Transport of circulating reduced glutathione (GSH) was studied at the basolateral side of the lens epithelium by using an in situ vascular e ye perfusion technique in guinea-pigs with rapid sampling to ensure de tecting initial uptakes. The unidirectional transport rates of [S-35]- GSH (4 nM) from plasma and aqueous into the epithelial cytosol were 0 . 046 +/- 0 . 003 and 6 . 88 +/- 0 . 39 min(-1), respectively. HPLC an alysis indicated that over 94% of [S-35]-GSH remained intact in the ep ithelium and cortex in the presence or absence of gamma-glutamyl trans peptidase inhibitor, serine berate. Simultaneous infusion of [S-35-cys teine]-GSH and [H-3-glycine]-GSH confirmed the non-involvement of gamm a-glutamyl transpeptidase in GSH transport across the lenticular membr anes by showing that S-35/H-3 ratio in the epithelium and cortex was t he same as in the aqueous and plasma. GSH epithelial influx was reduce d by 53% (P < 0 . 01) by 0 . 3 mM sulphobromophtalein-GSH, a GSH conju gate that does not inhibit the facilitative GSH transporter, RcGshT, r ecently found in the lens. At physiologic concentration of circulating GSH at 30 mu M, GSH epithelial influx was 0 . 77 nmol min(-1) g(-1); a t(1/2) of 85 . 4 hr was estimated if endogenous epithelial GSH had t o be replaced exclusively by plasma-derived GSH. The level of GSH in t he epithelium was increased by 38% (P < 0 . 05) by 1 hr arterial infus ion of GSH at 20 mM. The aqueous concentration of GSH under these cond itions was 1 . 2 mM so that accumulation in the epithelium occurred a greater than six-fold concentration gradient. It is concluded that: (a ) transport of GSH at the basolateral side of the epithelium is mediat ed by a concentrative mechanism distinct from RcGshT; (b) circulating GSH may represent a major source for epithelial GSH under physiologic conditions; and (c) the level of GSH in the epithelium can be manipula ted by exogenous GSH. (C) 1996 Academic Press Limited