Apical and basolateral 4F2hc and the amino acid exchange of L-DOPA in renal LLC-PK1 cells

• Published in: Amino acids 2005-11, Vol.29 (3), p.213-219
• Main Authors: Soares-da-Silva, P, Serrão, M. P
• Format: Article
• Language: English
• Subjects: Amino Acid Transport Systems - physiology; Amino acids; Amino Acids - metabolism; Animals; Biological Transport - drug effects; Biological Transport - physiology; carbon; Carbon Radioisotopes; Cell Polarity - physiology; Cells; Cells, Cultured; Fusion Regulatory Protein 1, Heavy Chain - drug effects; Fusion Regulatory Protein 1, Heavy Chain - genetics; Fusion Regulatory Protein 1, Heavy Chain - physiology; Gene Expression Regulation - drug effects; glycoproteins; Kidney - cytology; Kidney - drug effects; Kidney - metabolism; L-dopa; Levodopa - metabolism; Levodopa - pharmacokinetics; LLC-PK1 Cells; messenger RNA; oligonucleotides; Oligonucleotides, Antisense - pharmacology; Proteins; radionuclides; RNA, Messenger - drug effects; RNA, Messenger - genetics; RNA, Messenger - metabolism; Swine
• ISSN: 0939-4451; 1438-2199
• DOI: 10.1007/s00726-005-0242-5

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.