Intraocular transport of myoinositol

[2-H] Myoinositol accumidates in rabbit ciliary body-iris preparations in vitro against a concentration gradient. The transport system is energy and temperature dependent (Ql0 = 2.3) and demonstrates saturation kinetics (Km = 0.9 mM.). It is inhibited by ouabain, iodoacetate, phlorhizin, and shows requirements for Na, K+, and Ca. The transport system appears highly specific; various amino acids, ascorbic acid, glucoascorbic acid, and sugar alcohols were without effect on the accumulation of inositol. The stereoisomer scylloinositol was found to inhibit the transport of myoinositol. Dand x.-chiroinositols had no effect. The phosphate esters of inositol competitively inhibited transport of myoinositol. The steady state concentrations of inositol in the lens, ciliary body-iris, aqueous humors, and plasma were determined. The concentration in posterior aqueous was higher than in the anterior aqueous and still higher than in plasma. Evidence is presented to show that the transport of inositol across the blood-aqueous barrier in vivo is a carrier-mediated process and it is suggested that the high concentration of inositol in the aqueous humors is the result of active transport from plasma into posterior aqueous.