The Transport of ¹⁴C -Aminoisobutyric Acid in Galactose Cataracts in Rats and Rabbit Lenses Incubated in High Galactose Media

¹ Department of Ophthalmology and Oscar Johnson Institute, Washington University School of Medicine St. Louis, Mo.

The accumulation of ¹⁴C -aminoisobutyric (-AIB), a free and neutral amino acid, was markedly decreased in galactosemic rat lenses and in rabbit lenses incubated in vitro with 30 mM. d-galactose in the media. The ¹⁴C -AIB accumulation ratios were lower in galactosemic lenses studied in vivo than in vitro when compared to their controls. Rabbit lenses incubated for 4 hours or longer in high galactose media and transferred to galactose-free media had decreased ¹⁴C -AIB accumulation ratios when compared to controls. In kinetic experiments corrected for the increased ¹⁴C -AIB efflux, lenses incubated in 30 mM. galactose showed competitive inhibition of d-galactose (or its accumulated metabolite, galactitol) and -AIB accumulated by the lens. From the described results it is concluded that the effects of d-galactose on the transport and efflux of aAIB by the lens are exerted (1) mainly inside the lens, by d-galactitol or increased hydration, and on the Na⁺ dependent (ouabain-sensitive) (Na⁺ K⁺ ATPase dependent) fraction of -AIB transport into lens. (2) To a small degree outside the lens by a direct effect of d-galactose on the transporting site of -AIB in the lens. The decreased amino acid levels in lenses of galactose-fed rats appeared also related to similar depletions in the content of myo-inositol in such lenses. This cyclic alcohol has been found essential for the maintenance of amino acid transport by cells in vitro.