The characterisation and uptake of paraquat in cultured baboon kidney proximal tubule cells (bPTC)

A primary culture of baboon proximal tubule cells (bPTC) was prepared and c haracterised using LLC-PK1 cells of proximal tubule origin and MDCK cells o f distal tubule origin, as positive and negative references, respectively. The proximal tubular origin of the bPTC was determined by morphological stu dies, immunoperoxidase staining and the expression of proximal tubule marke rs alkaline phosphatase and gammaglutamyltransferase. The hypothesis that paraquat (PQ) is transported by the bPTC was investigat ed. The cytotoxic threshold for PQ in these cells was determined and compar ed to the LLC-PK1 and MDCK cells. Furthermore, this study investigated the transport of the monovalent cation tetraethyl ammonium (TEA) and the polyva lent cation cimetidine in the bPTC and demonstrated their effect on the cel lular uptake of PQ. The cytotoxic threshold of PQ in the bPTC, determined b y cellular viability studies using the method of Try-pan blue exclusion, is 0.05 mM at 2 h incubation. The LC50 after 24 h is 76, 61 and 455 muM for t he bPTC, LLC-PK, and MDCK cells, respectively. This indicates that proximal tubule cells are more susceptible to PQ toxicity compared to distal tubule cells, which is consistent with clinical PQ toxicity where renal damage is found predominantly in the proximal renal tubules. The cations PQ and cimetidine were actively transported by the bPTC. The up take of PQ (0.05 mM) commenced after 15 min whereas cimetidine (0.5 mM) upt ake was evident after 2 min. Furthermore, cimetidine was shown to compete w ith PQ for uptake in the bPTC, Coincubating PQ (0.05 mM) and cimetidine (0. 5 mM) for 60 min resulted in an approximate 50% decrease in PQ uptake. The cation TEA was not transported by the bPTC suggesting either a genetic mutation or complete absence of the transporter for TEA in the cells. The r esults suggest that PQ may be transported by the same cation transporter as cimetidine and not TEA, indicating PQ uptake in the bPTC to be via a polyv alent organic cation transporter.