Expression and functional involvement of organic anion transporting polypeptide subtype 3 (Slc21a7) in rat choroid plexus.
OBJECTIVE
It has been shown that transport(s) are involved in the uptake of estradiol 17beta glucuronide (E217betaG) by the choroid plexus (CP). The purpose of this study is to compare the substrate specificity of the transporter in the CP with those of rat organic anion transporting polypeptide 1 (rOatp1) and rOatp3.


METHODS
The expression of rOatp1 and rOatp3 in rat CP was confirmed by RT-PCR and Western blot analyses. The substrate specificity of rOatp1 and rOatp3 was compared using cDNA-transfected LLC-PK1 cells. The uptake of E217betaG by rat isolated CP was determined by centrifugal filtration technique.


RESULTS
PCR analyses demonstrated that the mRNA expression of rOatp3 was abundant in the CP, whereas that of rOatp1 was low. Immunohistochemical staining revealed that rOatp3 is expressed on the apical membrane of the CP. Kinetic parameters (Km and Ki values) of rOatp3 were similar to those for rOatp1. The results of mutual inhibition study suggest that E217betaG and taurocholate share the same mechanism in the CP. Corticosterone, estrone-3-sulfate and indomethacin are moderate inhibitors, but no effects by digoxin, p-aminohippurate, benzylpenicillin and cimetidine were observed.


CONCLUSIONS
rOatp3 is most possible candidate transporter involved in the uptake of organic anions on the brush border membrane of the choroid epithelial cells.
Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Hiroyuki
H
Kusuhara
Zhonggui
Z
He
Yoshinori
Y
Nagata
Yoshitane
Y
Nozaki
Takashi
T
Ito
Hiroyuki
H
Masuda
Peter J
PJ
Meier
Takaaki
T
Abe
Yuichi
Y
Sugiyama
D000818:Animals; D002831:Choroid Plexus / Q000378:metabolism*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D005786:Gene Expression Regulation; D018374:LLC-PK1 Cells; D008297:Male; D029362:Organic Anion Transporters, Sodium-Independent / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013552:Swine
D029362:Organic Anion Transporters, Sodium-Independent; D012333:RNA, Messenger; C421143:Slco1a5 protein, rat; C025483:estradiol-17 beta-glucuronide; D004958:Estradiol