ACELL June 45/6

Villalobos, Alice R., Judith T. Parmelee, and J. Larry Renfro. Choline uptake across the ventricular membrane of neonate rat choroid plexus. Am. J. Physiol. 276 (Cell Physiol. 45): C1288–C1296, 1999.—The uptake of [3H]choline from 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 ,5 at 1 min and as high as 70 at 30 min. Apical choline uptake was facilitated; the Km was ,50 μM. Several organic cations (e.g., hemicholinium-3 and N1methylnicotinamide) inhibited uptake. The reduction or removal of external Na1 or the addition of 5 mM LiCl had no effect on uptake. However, increasing external K1 concentration from 3 to 30 mM depolarized ventricular membrane potential (270 to 215 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 ,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 Na1 influx but is sensitive to plasma membrane electrical potential.