Transport of benzylpenicillin by the rat choroid plexus in vitro

To characterize the transport system by which benzylpenicillin, an organic anion, is accumulated by the isolated rat choroid plexus, kinetic analysis of benzylpenicillin transport was performed. Accumulation of benzylpenicillin was against an electrochemical potential gradient via a saturable process (Km = 58 microM and Vmax = 84 nmol/ml of tissue per min) that was inhibited by sulfhydryl reagents (p-hydroxymercuribenzoate and N-ethylmaleimide), metabolic inhibitors (KCN and 2,4-dinitrophenol) and anion exchange inhibitors (4-acetamide-4'-isothiocyanatostilbene-2,2'-disulfonic acid and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid), but is major transport system did not require the inward Na+ gradient. Organic anions, such as 5-hydroxyindoleacetic acid, homovanillic acid, p-aminohippuric acid and probenecid inhibited the accumulation of benzylpenicillin, whereas dipeptides did not affect it. Kinetic analysis of the accumulation of benzylpenicillin suggests that both phenoxymethylpenicillin and cefpiramide are also transported via the benzylpenicillin transport system. Other penicillin and cephalosporin derivatives inhibited the accumulation of benzylpenicillin with different affinities. Penicillin derivatives without dissociating groups in the side chain had the higher affinity for the benzylpenicillin transport system than other beta-lactam antibiotics did. Among penicillin derivatives examined, a good correlation (r = 0.92) was observed between the lipophilicity and the affinity for the benzylpenicillin transport system, whereas no correlation was observed among the cephalosporin derivatives. These findings suggest that the major transport system of benzylpenicillin in the rat choroid plexus is via a carrier-mediated active anion transport process which is distinct from that of dipeptides, and does not require the inward Na+ gradient.(ABSTRACT TRUNCATED AT 250 WORDS)