[Active transport of fluorescein in the choroid plexus of the brain and regulation of its rate by cyclic 3',5'-AMP].

With the aid of luminescent microscopy and microfluorimetry in vitro, the transport of labelled fluorescine into the structures of the brain lateral ventricles' chorioid plexus was studied in rabbits. An against-gradient pumping of fluorescine into the cytoplasm of the neuroepithelium cells and into the lumen of adjucent capillaries was shown to occur in the chorioid plexus. Such accumulation of fluorescine proceeds in the active transport way with participation of a carrier. The active transport system is congenial to fluorescine - Km = 4-10(-5) M, which renders even small amounts of this substance to be quickly removed from the milieu. The fluorescine-transporting system fulfills transition of other organic acids as well. The system of organic acids active transport is, apparently, localized in the apical and basal membranes of the neuroepithelial cells surrounding the plexus' filia which makes the concentration of transported acid in the neuroepithelial cells higher than in milieu, and in the capillaries' lumen higher than in the cytoplasm. An enzyme system adenylcyclasa-phosphodiesterase was found in the chorioid plexus' neuroepithelium. The system participates in regulation of velocity of the organic acids transport by means of changing the intracellular concentration 3',5'-AMP.