Abstract
The role of P-glycoprotein (P-gp) in the basal-to-apical uptake and flux of l-3,4-dihydroxyphenylalanine (l-dopa) was studied in LLC-PK1 and LLC-GA5 Col300 cells, a renal cell line expressing the human P-gp in the apical membrane. In the absence of verapamil, LLC-GA5 Col300 cells accumulate less calcein (0.5 μM) than do LLC-PK1 cells. In LLC-PK1 cells, pretreatment with verapamil (25 μM) for 30 min increased the rate of accumulation of calcein by 5-fold, whereas in LLC-GA5 Col300 cells, no significant change in the rate of accumulation of calcein was observed. Exposure for 3 h to verapamil (25 μM) was found to increase the rate of accumulation of calcein by 2.5-fold in LLC-PK1cells and by 3.7-fold in LLC-GA5 Col300 cells. A 30-min exposure to UIC2 (3 μg/ml) or verapamil (25 μM) increased l-dopa accumulation in LLC-PK1 cells by 27 ± 4 and 88 ± 14% and reduced l-dopa apical extrusion by 29 ± 4 and 23 ± 1%, respectively. The exposure of LLC-GA5 Col300 cells to UIC2 (3 μg/ml) or verapamil (25 μM) for 30 min produced no significant changes in cell accumulation and apical extrusion ofl-dopa. A more prolonged exposure (3 h) to UIC2 or verapamil resulted in a marked increase in l-dopa accumulation in the cell (105 ± 13 and 146 ± 24% increase) and a pronounced decrease (91 ± 1 and 92 ± 1% reduction) in the apical extrusion of l-dopa. It is concluded that LLC-PK1 cells are endowed with P-gp and that the outward transfer of l-dopa at the apical cell border in both LLC-PK1 and LLC-GA5 Col300 cells is in part promoted through this transporter.
Footnotes
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Send reprint requests to: Dr. P. Soares-da-Silva, Institute of Pharmacology & Therapeutics, Faculty of Medicine, 4200 Porto, Portugal. E-mail: Patricio.Soares{at}mail.telepac.pt
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↵1 This work was supported by Grant PRAXIS/SAU/123/96 from Fundação para a Ciência e a Tecnologia.
- Abbreviations:
- CsA
- cyclosporine A
- P-gp
- P-glycoprotein
- l-dopa
- l-3,4-dihydroxyphenylalanine
- AADC
- aromatic l-amino acid decarboxylase
- Rh123
- rhodamine 123
- AM
- acetoxymethyl ester
- Received September 30, 1999.
- Accepted December 16, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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