Myo-inositol transport into endothelial cells derived from nervous system microvessels

Abstract

Myo-inositol, the precursor in the biosynthesis of inositol phospholipids and inositol phosphates, is found in many tissues at concentrations well above its concentration in the plasma, but the highest concentrations are found in the central nervous system and the neuroretina. We describe an active, sodium gradient-dependent transport of myo-inositol into cultured endothelial cells derived from bovine retinal microvessels. Transport is inhibited by cytochalasin B, and phloridzin > phloretin. Mannitol, sorbitol, and fructose do not inhibit uptake, but -galactose inhibits uptake > -glucose > -glucose. The apparent Km of this transport system is 311 +/- 47 (S.D.) [mu]M and the apparent Vmax is 40.8 +/- 2.8 (S.D.) pmol[middle dot]mg protein-1[middle dot]min-1. This transport system may be a key in the maintenance of high tissue concentrations as it could concentrate myo-inositol from the plasma into the extracellular spaces of the eye and central nervous system.