Measurement of retinal permeability to sodium fluorescein in vitro

Fluorescein permeabilities of isolated dog retinal pigment epithelium (RPE)-choroid and sensory retina were measured individually. Retina to choroid (outward) permeability of sodium fluorescein was significantly larger than choroid to retina (inward) permeability at RPE-choroid under both open- and short-circuit conditions. Outward permeability was decreased by the addition of 10(-3) M KCN and of 10(-4) M probeneside but was not affected by 10(-6) M ouabain. These drugs decreased transepithelial potential and short-circuit current. No directional difference of fluorescein permeability for sensory retina was found. Active transport of fluorescein across RPE from retina to choroid is suggested. Fluorescein permeability of sensory retina was larger than inward but less than outward permeability of RPE-choroid. The result indicates that the sensory retina acts as a diffusion barrier for sodium fluorescein.