CHOLINE UPTAKE BY CEREBRAL CAPILLARY ENDOTHELIAL-CELLS IN CULTURE

Abstract: A passage of choline from blood to brain and vice versa has been demonstrated in vivo. Because of the presence of the blood‐brain barrier, such passage takes place necessarily through endothelial cells. To get a better understanding of this phenomenon, the choline transport properties of cerebral capillary endothelial cells have been studied in vitro. Bovine endothelial cells in culture were able to incorporate [3H]choline by a carrier‐mediated mechanism. Nonlinear regression analysis of the uptake curves suggested the presence of two transport components in cells preincubated in the absence of choline. One component showed a Km of 7.59 ± 0.8 μM and a maximum capacity of 142.7 ± 9.4 pmol/2 min/mg of protein, and the other one was not saturable within the concentration range used (1–100 μM). When cells were preincubated in the presence of choline, a single saturable component was observed with a Km of 18.5 ± 0.6 μM and a maximum capacity of 452.4 ± 42 pmol/2 min/mg of protein. [3H]Choline uptake by endothelial cells was temperature dependent and was inhibited by the choline analogs hemicholinium‐3, deanol, and AF64A. The presence of ouabain or 2,4‐dinitrophenol did not affect the [3H]choline transport capacity of endothelial cells. Replacement of sodium by lithium and cell depolarization by potassium partially inhibited choline uptake. When cells had been preincubated without choline, recently transported [3H]choline was readily phosphorylated and incorporated into cytidine‐5′‐diphosphocholine and phospholipids; however, under steady‐state conditions most (63%) accumulated [3H]choline was not metabolized within 1 h. Only part of the labelled intracellular free choline was transported back into the incubation medium. Because of their special location, transport properties, and metabolism, cerebral capillary endothelial cells may provide a gating mechanism that can contribute to the physiological control of choline concentration in the brain extracellular fluid. Copyright © 1990, Wiley Blackwell. All rights reserved