Renal organic cation and nucleoside transport.
We previously reported that the rat organic cation transporter rOCT1 could transport the nucleoside analog deoxytubercidin (dTub) (Chen R, Nelson JA. Biochem Pharmacol 2000;60:215-9). The cationic form of dTub (dTub(+)) appeared to be the true substrate of rOCT1. We also reported that although rOCT2 is similar to rOCT1, it does not transport dTub at pH 7.4. In this study, we measured the K(m) and V(max) values of dTub(+) uptake at a reduced pH (pH 5.4) for both rOCT1 and rOCT2. The difference in substrate activity appears due, in large part, to a poor affinity of rOCT2 for dTub(+). The transport efficiency estimated by V(max)/K(m) values for rOCT2 was only 6% that of rOCT1. Chimeras constructed between rOCT1 and rOCT2 revealed that the difference in dTub binding lies within transmembrane domains 2-7. To evaluate the potential of OCT1 in the renal secretion of dTub, tissue distribution and urinary excretion of dTub in OCT1 knockout mice were measured. No significant difference was observed in renal elimination, plasma level, and tissue distribution of dTub between the knockout and the wild-type mice. Therefore, dTub is a good substrate for OCT1; however, OCT1 does not appear to be necessary for its renal secretion.
Chen
Rong
R
Division of Pediatrics and Department of Experimental Therapeutics, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA.
Jonker
Johan W
JW
Nelson
J Arly
JA
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D017136:Ion Transport; D007668:Kidney / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D033703:Nucleoside Transport Proteins; D009865:Oocytes / Q000378:metabolism; D027701:Organic Cation Transport Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D027702:Organic Cation Transporter 1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000075102:Organic Cation Transporter 2; D014162:Transfection; D014372:Tubercidin / Q000031:analogs & derivatives* / Q000378:metabolism*; D014982:Xenopus laevis
D002352:Carrier Proteins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D027701:Organic Cation Transport Proteins; D027702:Organic Cation Transporter 1; D000075102:Organic Cation Transporter 2; C491012:Slc22a2 protein, mouse; C053222:2'-deoxytubercidin; D014372:Tubercidin