We have investigated the transport properties of cultured porcine chor
oid plexus cells grown on permeable membranes and in serum-free medium
. Withdrawal of serum yielded cell cultures with permeabilities low en
ough to establish and maintain a pH-gradient between the two compartme
nts of the filter system and to allow apical fluid secretion. This bec
ame possible because of ten-fold increased electrical resistance of 17
00 Omega cm(2) in the absence of serum. These plexus epithelial cells
transported phenol red, fluorescein, riboflavin and penicillin G from
the apical to the basolateral side. K-M values and v(max) were determi
ned and come close to in vivo values. Competitive inhibition with prob
enicid showed that the organic anion transporter is involved. Riboflav
in transport however was not completely inhibited and did not respond
quantitatively to the stilben derivate SITS that blocks the Cl-/HCO3-
exchanger. We assume that an additional transport system exists for ri
boflavin. Ascorbic acid and myo-inositol were transported from the bas
olateral to the apical side in vitro which strongly resembles the in v
ivo transport from the blood to the cerebrospinal fluid. Again the exp
erimental in vitro K-M values come close to the in vivo values. The es
tablished epithelial cell culture model thus closely mimics the blood-
CSF-barrier and may be a useful tool to further elucidate transport to
and from the brain. (C) 1998 Elsevier Science B.V. All rights reserve
d.