[Kinetic study of movement of fluorescein across the isolated rabbit retinal pigment epithelium--choroid].

Using an Ussing-type chamber, the transport of fluorescein (F) across the isolated retinal pigment epithelium (RPE)-choroid of the rabbit was studied. The outward movement (from the vitreous to the choroidal side) of F was significantly greater than the inward movement (from the choroidal to the vitreous side) and was suppressed by the application of 10(-4)M probenecid, 30mM hippurate or 5mM iodipamide to 41%, 45% or 39% of the control, respectively, while the inward movement was not affected by any of these agents. As the F concentration in the chamber increased, the inward movement of F also increased in a linear fashion, but the outward movement showed nonlinearity. The difference between the outward and inward movement of F was thought to represent the net flux of F across the RPE-Choroid and this value showed nonlinearity and saturation as the F concentration increased. The Lineweaver-Burk plot of the reciprocals of the net flux of F concentration gave the apparent Km of 4.5 x 10(-5)M and apparent Vmax of 2.27 nmoles/hr/cm2, which suggested that the F transport system in the rabbit RPE-Choroid had a greater affinity to the substrate but lower transporting capacity as compared with the F transport system in the rabbit iris-ciliary body or the ascorbate transport system in the iris-ciliary body.