Over-expression of renal LAT1 and LAT2 and enhanced L-DOPA uptake in SHR immortalized renal proximal tubular cells.
BACKGROUND
Spontaneously hypertensive rats (SHR) may have an increased renal production of dopamine. LAT2 promotes L-DOPA renal uptake, and this may determine the rate of dopamine synthesis. The present study evaluated L-DOPA inward and outward transfer in immortalized renal proximal tubular epithelial cells of SHR and Wistar-Kyoto rats (WKY).


METHODS
Uptake of [(14)C]-L-DOPA was initiated by the addition of 1 mL Hanks' medium with a given concentration of the substrate. The apical fractional outflow of intracellular [(14)C]-L-DOPA was evaluated in cells loaded with [(14)C]-L-DOPA for 6 minutes, and then the corresponding efflux was monitored over 12 minutes. The presence of LAT1 and LAT2 transcripts and protein in WKY and SHR cells was examined, respectively, by reverse transcription-polymerase chain reaction (RT-PCR) and immunobloting.


RESULTS
LAT2 in WKY cells contributed almost exclusively for [(14)C]-L-DOPA uptake. In SHR cells [(14)C]-L-DOPA uptake was 25% through system B(0), 25% through LAT2 (resulting from inhibition by 1 mmol/L glycine, L-alanine, L-serine, and L-threonine), and the remaining 50% through LAT1. The efflux of [(14)C]-L-DOPA from WKY and SHR cells corresponded to approximately 65% and approximately 25%, respectively, of the amount accumulated in the cells. The LAT1 and LAT2 transcripts were present in both SHR and WKY cells, but the abundance of both LAT1 and LAT2 proteins in SHR cells was greater than in WKY cells.


CONCLUSIONS
Differences in L-DOPA handling between SHR and WKY cells may result from over-expression of LAT1 and LAT2 transporters in the former. The unique role of Na(+)-dependent transporters (system B(0)) in SHR cells also contributes to the enhanced L-DOPA uptake in these cells.
Pinho
Maria João
MJ
Institute of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal.
Serrão
Maria Paula
MP
Gomes
Pedro
P
Hopfer
Ulrich
U
Jose
Pedro A
PA
Soares-da-Silva
P
P
D027182:Amino Acid Transport System y+ / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002461:Cell Line, Transformed; D027301:Fusion Regulatory Protein 1, Light Chains / Q000235:genetics / Q000378:metabolism*; D006973:Hypertension / Q000378:metabolism* / Q000473:pathology; D007668:Kidney / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism* / Q000473:pathology; D027283:Large Neutral Amino Acid-Transporter 1 / Q000235:genetics / Q000378:metabolism*; D007980:Levodopa / Q000493:pharmacokinetics*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY
D027182:Amino Acid Transport System y+; D027301:Fusion Regulatory Protein 1, Light Chains; D027283:Large Neutral Amino Acid-Transporter 1; D012333:RNA, Messenger; C486582:Slc7a8 protein, rat; D007980:Levodopa