Characterisation and uptake of paraquat by rat renal proximal tubular cells in primary culture

1 Uptake of the herbicide paraquat (PQ), by rat proximal tubular cells (PTC) in primary culture grown on a collagen coated support was investigated. 2 The uptake of PQ by PTC was predominantly from the basolateral side. The basolateral uptake of PQ was saturable with time and increasing concentrations, energy dependent and could be inhibited by certain organic cations. Using Michaelis Menten kinetics, the apparent Km was 778 +/- 241 mu M and V-max was 0.97 +/- 0.24 pmol/mu g protein/15 min for the basolateral uptake of PQ. Cimetidine (5.7 +/- 0.4 pg/mu g protein/30 min, P < 0.001) was the most potent inhibitor of PQ uptake, followed by quinine (6.5 +/- 0.4 pg/mu g protein/30 min, P < 0.01) and then tetraethylammonium (8.2 +/- 0.5 pg/mu g protein/30 min, P < 0.05) when compared with control (11 +/- 1 pg/mu g protein/30 min). N-methylnicotinamide, p-aminohippurate and putrescine did not inhibit the basolateral uptake of PQ. The sodium hydrogen exchange inhibitors, amiloride and its analogue, 5-(N,N hexamethylene) amiloride (HMA) inhibited both the apical and basolateral uptake of PQ. 3 The apical uptake of PQ was not saturable with increasing concentrations and was not inhibited by 2,4-dinitrophenol, but it was reduced by cimetidine (P < 0.01), quinine (P < 0.05) and a sodium potassium ATPase inhibitor, ouabain (P < 0.01). 4 It is concluded that PQ was taken up from the basolateral side of primary cultured rat PTC by an energy dependent transport system.