Inhibition of basolateral transport and cellular accumulation of cDDP and N-acetyl-L-cysteine-cDDP by TEA and PAH in the renal proximal tubule

Purpose: The objective of this study was to determine the effect of para-aminohippurate (PAH) and tetraethylammonium (TEA) on basolateral cellular accumulation (C Pt ) and bath-to-lumen transepithelial transport rates (J B→L ) of platinum from cisplatin (cDDP) and a conjugate of cDDP, N-acetyl-L-cysteine-cDDP (NAC-cDDP), in S 1 , S 2 , and S 3 segments of the rabbit proximal tubule. Methods: Cellular accumulations and transport rates were determined using the isolated perfused tubule technique and samples were analyzed by ICP-MS. Results: First, to establish the control data, each tubular segment was bathed in free cDDP (2 mM) which resulted in no observable toxicity. Next, TEA (4 mM) was added to the bathing solution containing cDDP. This resulted in a reduction in platinum J B→L by approximately 75% in the S 1 segment and 50% in the S 2 and S 3 segments. C Pt was reduced by 80-90% in relation to control values with no observable changes in toxicity. In the next experiment, exposure of the basolateral membrane to NAC-cDDP (2 mM) elicited pronounced toxicity after 20-30 min of perfusion. The J B→L for NAC-cDDP was similar for each of the three nephron segments. There were no significant differences in the ability of these three segments to accumulate NAC-cDDP, but the conjugate increased uptake of platinum by 200-300% in the S 1 and S 2 segments, with no significant change in the S 3 segments, compared cDDP control values. The presence of PAH (4 mM) in the bathing solution significantly reduced J B→L (by approximately 90%) for NAC-cDDP in all segments and the C Pt by approximately 80%. This also abrogated the NAC-cDDP-induced toxicity. Conclusions: There was axial heterogeneity among the basolateral membranes of the S 1 , S 2 , and S 3 segments of the proximal tubule in accumulating free cDDP and transport of NAC-cDDP. Generally, the NAC-cDDP molecule was transported more avidly than free cDDP across the basolateral membrane, except in the S 3 segment, where accumulation was similar to that of free cDDP. It is concluded that a PAH-sensitive organic anion transporter is involved in the accumulation of NAC-cDDP at the basolateral membrane and a TEA-sensitive organic cation transport system is involved in the accumulation of free cDDP.