Apical and basolateral 4F2hc and the amino acid exchange of L-DOPA in renal LLC-PK1 cells.
The present study aimed to examine the presence and define the role of 4F2hc, a glycoprotein associated with the LAT2 amino acid transporter, in L-DOPA handling by LLC-PK1 cells. For this purpose we have measured the activity of the apical and basolateral inward and outward transport of [14C] L-DOPA in cell monolayers and examined the influence of 4F2hc antisense oligonucleotides on [14C] L-DOPA handling. The basal-to-apical transepithelial flux of [14C] L-DOPA progressively increased with incubation time and was similar to the apical-to-basal transepithelial flux. The spontaneous and the L-DOPA-stimulated apical fractional outflow of [14C] L-DOPA were identical to that through the basal cell side. The L-DOPA-induced fractional outflow of [14C] L-DOPA through the apical or basal cell side was accompanied by marked decreases in intracellular levels of [14C] L-DOPA. In cells treated with an antisense oligonucleotide complementary to 4F2hc mRNA for 72 h, [14C] L-DOPA inward transport and 4F2hc expression were markedly reduced. Treatment with the 4F2hc antisense oligonucleotide markedly decreased the spontaneous fractional outflow of [14C] L-DOPA through the apical or the basal cell side. It is likely that the Na+-independent and pH-sensitive uptake of L-DOPA include the hetero amino acid exchanger LAT2/4F2hc, which facilitates the trans-stimulation of L-DOPA and its outward transfer at both the apical and basal cell sides.
Soares-da-Silva
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Institute of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal. psoaresdasilva@netcabo.pt
Serrão
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MP
D026905:Amino Acid Transport Systems / Q000502:physiology; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002250:Carbon Radioisotopes; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D027282:Fusion Regulatory Protein 1, Heavy Chain / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018374:LLC-PK1 Cells; D007980:Levodopa / Q000378:metabolism* / Q000493:pharmacokinetics; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D013552:Swine
D026905:Amino Acid Transport Systems; D000596:Amino Acids; D002250:Carbon Radioisotopes; D027282:Fusion Regulatory Protein 1, Heavy Chain; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D007980:Levodopa