TRANSEPITHELIAL TRANSPORT OF ASCORBIC-ACID BY THE ISOLATED INTACT CILIARY EPITHELIAL BILAYER OF THE RABBIT EYE

The purpose of these experiments was to test whether the isolated inta ct epithelial bilayer derived from rabbit ciliary processes transports ascorbic acid and to what degree the transport rate in vitro correspo nds to the in vivo process. The intact ciliary epithelial bilayer of t he rabbit eye isolated by perfusion was mounted in a particularly cons tructed Ussing type chamber. Fluxes were measured by additions of C-14 ascorbate to the hemichamber on either the pigmented epithelium (PE) or the nonpigmented epithelium (NPE) side where equal concentrations o f ascorbate from .02 to 2.0 mM were present. Samples were taken at int ervals thereafter and counted in a liquid scintillation counter. The e xperiments were done under short circuit conditions to avoid the possi ble influence of fluctuating currents upon the movement of ascorbate. Like the earlier iris ciliary body preparations, separation of ascorba te fluxes is also done by the isolated intact ciliary epithelial bilay er, and the transport of ascorbic acid proceeds by saturation kinetics . The uptake process is accomplished entirely by the pigmented epithel ium (PE). The Km of the process is 0.97 mM, and Vmax was valued at 130 nM/L/hr. Thus, assuming an aqueous flow rate of 2 mu l/min, the trans fer of ascorbic acid across the bilayer occurs at a rate required to m aintain the ordinary millimolar concentration of ascorbic acid in the aqueous humor found in vivo.