RT Journal Article
SR Electronic
T1 The blood-retinal barrier: leucine transport by the retinal pigment epithelium
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 2823
OP 2828
DO 10.1523/JNEUROSCI.06-10-02823.1986
VO 6
IS 10
A1 Sellner, PA
YR 1986
UL http://www.jneurosci.org/content/6/10/2823.abstract
AB The transport of leucine across the isolated bullfrog pigment epithelium-choroid was studied in a modified Ussing chamber. With the same concentration of leucine on both sides of the tissue, there was a net flux in the apical-to-basal (retina-to-choroid) direction. The concentration dependence of the apical-to-basal flux comprised at least 2 components: a carrier-mediated flux, with an apparent Km of 0.76 mM and a Vmax of 298 nmol/cm2/hr, and a linear component with a slope of 33.4 cm/hr. The basal-to-apical flux was linear to 10 mM leucine, with a slope of 60 cm/hr. In the absence of Na+, the apical-to-basal flux was inhibited 20%, while the basal-to-apical flux was unaffected. The apical-to-basal flux could be inhibited to the level of the basal-to- apical flux by removing glucose from the solution and adding KCN. Otherwise both fluxes were relatively unaltered by metabolic poisons. There appear to be 3 contributors to the apical-to-basal flux: a weakly Na+-dependent carrier, a linear component (diffusion), and a countertransport mechanism. The basal-to-apical flux must have 2 linear mechanisms, diffusion to the same extent as the opposite flux, and possibly pinocytosis.