Uptake of L-3,4-dihydroxyphenylalanine and dopamine formation in cultured renal epithelial cells

• Type: Article in International Scientific Journal
• Date: 1997

Authors

soares-da-silva, p (Author) FMUP; vieira-coelho, ma (Author) Other; Maria Paula Serrão (Author) REIT

Journal

Title: Biochemical Pharmacology

Vol. 54

Pages: 1037-1046

ISSN: 0006-2952

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 13 Citations

Scopus - 14 Citations

Other information

Authenticus ID: P-001-ABE

DOI: 10.1016/s0006-2952(97)00318-3

Abstract (EN): In the presence of benserazide (50 mu M), L-3,4-dihydroxyphenylalanine (L-DOPA) was rapidly accumulated in both LLC-PK1 and OK cells; equilibrium was attained at 30 min of incubation. For these LLC-PK, and OK cells, the analysis revealed a rate constant of inward transport (k(in) in pmol/mg protein/min) of 3.6 +/- 0.4 and 18.1 +/- 0.3 and a rate constant of outward transport (k(out) in pmol/mg protein/min) of 1.0 +/- 0.1 and 5.2 +/- 0.1, respectively. Nonlinear analysis of the saturation curves for LLC-PK, and OK cells revealed a K-m (in mu M) of 86 +/- 12 and 14 +/- 4, respectively. The cellular accumulation of the substrate was temperature-dependent and stereoselective. Aromatic L-amino acid decarboxylase (AAAD) activity was determined in cell homogenates; nonlinear analysis of the saturation curves revealed, for LLC-PK1 and OK cells, a K-m (in mu M) of 1866 +/- 107 and 845 +/- 153 and a V-max (in nmol/mg protein/15 min) of 4.4 +/- 0.1 and 0.9 +/- 0.1, respectively. In the absence of benserazide, only a limited amount of the L-DOPA taken up was decarboxylated to dopamine in cell monolayers; the K-m value (in mu M) for decarboxylation of intracellular L-DOPA in LLC-PK1 and OK cells was 61 +/- 14 and 108 +/- 36, respectively. A low amount of newly formed dopamine was found to escape to the apical bathing fluid. This outward transfer of newly formed dopamine was a nonsaturable process up to 300 mu M intracellular dopamine. In conclusion, the data presented here show that OK cells are endowed with a more efficient L-DOPA uptake system than LLC-PK1 cells, but the latter are endowed with a significantly higher AAAD activity than OK cells. In both cell lines, intracellular L-DOPA is rapidly converted to dopamine, some of which diffuses out of the cell. (C) 1997 Elsevier Science Inc.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 10