CHARACTERIZATION AND UPTAKE OF PARAQUAT BY RAT RENAL PROXIMAL TUBULARCELLS 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 inves tigated. 2 The uptake of PQ by PTC was predominantly from the basolate ral side. The basolateral uptake of PQ was saturable with time and inc reasing concentrations, energy dependent and could be inhibited by cer tain 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) a nd 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-me thylnicotinamide, p-aminohippurate and putrescine did not inhibit the basolateral uptake of PQ. The sodium hydrogen exchange inhibitors, ami loride and its analogue, 5-(N,N hexamethylene) amiloride (HMA) inhibit ed both the apical and basolateral uptake of PQ. 3 The apical uptake o f PQ was not saturable with increasing concentrations and was not inhi bited 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 basolater al side of primary cultured rat PTC by an energy dependent transport s ystem.