Na+-independent transporters, LAT-2 and b0,+, exchange L-DOPA with neutral and basic amino acids in two clonal renal cell lines.
The present study examined the functional characteristics of L-DOPA transporters in two functionally different clonal subpopulations of opossum kidney (OKLC and OKHC) cells. The uptake of L-DOPA was largely Na+-independent, though in OKHC cells a minor component (approximately 15%) required extracellular Na+. At least two Na+-independent transporters appear to be involved in L-DOPA uptake. One of these transporters has a broad specificity for small and large neutral amino acids, is stimulated by acid pH and inhibited by 2-aminobicyclo(2,2,l)-heptane-2-carboxylic acid (BCH; OKLC, Ki = 291 mM; OKHC, Ki = 380 mM). The other Na+-independent transporter binds neutral and basic amino acids and also recognizes the di-amino acid cystine. [14C]-L-DOPA efflux from OKLC and OKHC cells over 12 min corresponded to a small amount of intracellular [14C]-L-DOPA. L-Leucine, nonlabelled L-DOPA, BCH and L-arginine, stimulated the efflux of [14C]-L-DOPA in a Na+-independent manner. It is suggested that L-DOPA uses at least two major transporters, systems LAT-2 and b0,+. The transport of L-DOPA by LAT-2 corresponds to a Na+-independent transporter with a broad specificity for small and large neutral amino acids, stimulated by acid pH and inhibited by BCH. The transport of L-DOPA by system b0,+ is a Na+-independent transporter for neutral and basic amino acids that also recognizes cystine. LAT-2 was found equally important at the apical and basolateral membranes, whereas system b0,+ had a predominant distribution in apical membranes.
Gomes
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P
Institute of Pharmacology & Therapeutics, Faculty of Medicine, 4200-319 Porto, Portugal.
Soares-da-Silva
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P
D024361:Amino Acids, Basic / Q000378:metabolism*; D000598:Amino Acids, Cyclic / Q000494:pharmacology; D021542:Amino Acids, Neutral / Q000378:metabolism*; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D002414:Cations, Monovalent; D002460:Cell Line; D002999:Clone Cells; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015259:Dopamine Agents / Q000493:pharmacokinetics*; D027301:Fusion Regulatory Protein 1, Light Chains / Q000378:metabolism*; D007668:Kidney / Q000166:cytology; D007980:Levodopa / Q000493:pharmacokinetics*; D009893:Opossums; D011493:Protein Kinase C / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012964:Sodium; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D015091:beta-Alanine / Q000031:analogs & derivatives* / Q000494:pharmacology
D024361:Amino Acids, Basic; D000598:Amino Acids, Cyclic; D021542:Amino Acids, Neutral; D015220:Calcium Channels; D002414:Cations, Monovalent; D015259:Dopamine Agents; D027301:Fusion Regulatory Protein 1, Light Chains; D017923:Sodium-Hydrogen Exchangers; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; D007980:Levodopa; D012964:Sodium; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase