Choline uptake across the ventricular membrane of neonate rat choroid plexus

The uptake of [H-3]choline fi om the cerebrospinal fluid (CSF) side of the rat neonatal choroid plexus was characterized in primary cultures of the choroidal epithelium grown on solid supports. Cell-to-medium concentration ratios were similar to 5 at 1 min and as high as 70 at 30 min. Apical choline uptake was facilitated; the K-m was similar to 50 mu M. Several organic cations (e.g., hemicholinium-3 and N-1-methylnicotinamide) inhibited uptake. The reduction or removal of external Na+ or the addition of 5 mM LiCl had no effect on uptake. However, increasing external K+ concentration fi om 3 to 30 mM depolarized ventricular membrane potential (-70 to -15 mV) and reduced uptake to 45% of that for the control. Treatment with 1 mM ouabain or 2 mM BaCl2 reduced uptake 45%, and intracellular acidification reduced uptake to similar to 90% of that for controls. These data indicate that the uptake of choline from CSF across the ventricular membrane of the neonatal choroidal epithelium is not directly coupled to Na+ influx but is sensitive to plasma membrane electrical potential.