Vol. 293, Issue 2, 697-704, May 2000

Outward Transfer of Dopamine Precursor L-3,4-Dihydroxyphenylalanine (L-dopa) by Native and Human P-glycoprotein in LLC-PK₁ and LLC-GA5 Col300 Renal Cells¹

Patrício Soares-da-Silva and Maria Paula Serrão

Institute of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal

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-PK₁ cells 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 of L-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.