Handling of cysteine S-conjugates of methylmercury in MDCK cells expressing human OAT1.
BACKGROUND
The activity of the organic anion transporter 1 (OAT1) has been implicated recently in the basolateral uptake of thiol conjugates of inorganic mercury in renal proximal tubular cells. However, very little is known about the role of OAT1 in the renal epithelial transport of organic forms of mercury, such as methylmercury (CH(3)Hg(+)), especially when it is in the form of the cysteine (Cys) S-conjugate of methylmercury (CH(3)Hg-Cys), which is believed to be a biologically relevant form of mercury.


METHODS
Accordingly, the present study, was designed to characterize the transport of CH(3)Hg-Cys in Madin-Darby canine kidney (MDCK) cells transfected stably with the human isoform of OAT1 (hOAT1) and in proximal tubular-derived NRK-52E cells.


RESULTS
Data on saturation kinetics, time dependency, substrate specificity, and temperature dependency demonstrate that CH(3)Hg-Cys is transported by hOAT1. Substrate-specificity data from the control cells also show that CH(3)Hg-Cys is a substrate of one or more transporter(s) that is/are not hOAT1. Additional findings indicate that at least one amino acid transport system is involved in the uptake of CH(3)Hg-Cys in MDCK cells. Furthermore, in the presence of cytotoxic concentrations of CH(3)Hg-Cys, rates of survival were lower in hOAT1-transfected cells than in wild-type control cells.


CONCLUSIONS
The present data demonstrate clearly that CH(3)Hg-Cys is indeed a transportable substrate of OAT1. Moreover, the collective findings from the MDCK cells and NRK-52E cells infer that CH(3)Hg-Cys is a likely transportable mercuric species in proximal tubular epithelial cells that is taken up in vivo by both OAT1 and amino acid transporters.
Zalups
Rudolfs K
RK
Division of Basic Medical Sciences, Mercer University, School of Medicine, Macon, Georgia 31207, USA. zalups_rk@mercer.edu
Ahmad
Sarfaraz
S
D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003545:Cysteine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000633:toxicity; D003998:Dicarboxylic Acids / Q000494:pharmacology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D005977:Glutarates / Q000494:pharmacology; D006801:Humans; D007668:Kidney / Q000166:cytology; D007930:Leucine / Q000494:pharmacology; D008767:Methylmercury Compounds / Q000493:pharmacokinetics* / Q000633:toxicity; D027362:Organic Anion Transport Protein 1 / Q000235:genetics / Q000378:metabolism*; D011339:Probenecid / Q000494:pharmacology; D013696:Temperature; D014162:Transfection; D014316:Tritium; D014528:Uricosuric Agents / Q000494:pharmacology; D010130:p-Aminohippuric Acid / Q000493:pharmacokinetics
D003998:Dicarboxylic Acids; D005977:Glutarates; D008767:Methylmercury Compounds; D027362:Organic Anion Transport Protein 1; D014528:Uricosuric Agents; D014316:Tritium; C030589:methylmercury cysteine; D007930:Leucine; D003545:Cysteine; D011339:Probenecid; D010130:p-Aminohippuric Acid