Ochratoiio transport across the peritubular membrane of rabbit proximal tubule

Ochratoxm A (OTA) is a widespread mycotoxin with the kidney as its main target. We used single rabbit tubules, isolated by dissection without the use of enzymatic agents, to examine the peritubular transport of OTA. Epifluorescence microscopy was used to measure uptake of OTA into single tubule segments attached to a cover-slip mounted in a perfusion chamber on the stage of an inverted microscope (excitation at 377 nm and emission at 440 nm with fluorescence output monitored by photon counting). Uptake and efflux of OTA were measured following rapid changes of the bathing medium at 37° C. Uptake of OTA in S2 segments exceeded that in S3 segments, a pattern consistent with an interaction of OTA with the peritubular organic anion transporter. Consistent with this hypothesis, OTA inhibited [³H] para-amtnohippurate (PAH) uptake into single S2 segments by 95% with an apparent inhibitory constant (Kj) of 1.7 uM. The reciprocal inhibition of OTA uptake by PAH was not as effective, with 10 mM PAH reducing OTA uptake by only 50%. A 500 uM concentration of probenecid did, however, reduce OTA uptake by 95%. Other organic anions, including Suorescein (100 μM) , octanoate (100 uM) and uric acid (ImM), varied in inhibitory effectiveness, reducing OTA uptake by 75%, 90% and 10% respectively. Efflux of OTA from single S2 tubule segments was transstimulated by PAH, fiuorescein and octanoate in the bath. These results suggest that peritubular OTA transport involves the organic anion transporter and at least one other mediated pathway. (NTH ES-06756).