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Vol. 287, Issue 1, 13-20, October 1998
Physiologisches Institut, Universität Würzburg,
Würzburg, Germany
Ochratoxin A (OTA) is a widespread mycotoxin, which is nephrotoxic and
carcinogenic. Because a decline in net-secretion of para-aminohippuric acid (PAH) was observed after chronic OTA
exposition in vivo, we investigated the effect of OTA on
proximal-tubule-derived opossum kidney (OK) cells. OTA up to
10
5 mol/liter had no acute effect on PAH transport when
bovine serum albumin (BSA) was present. By contrast, 72-hr incubation
of OK cells led to a decrease of PAH transport with half-maximal
inhibition at 6 · 10
7 mol/liter for
transepithelial secretion and 6 · 10
8 mol/liter
for basolateral uptake of PAH. Incubation of OK cells with
10
6 mol/liter OTA for 72 hr reduced the affinity of PAH
uptake, and decreased the maximum secretion rate to one-fifth of
control values. Apical uptake of amino acids and basolateral uptake of
glutarate were not affected. In addition, no signs of general toxic
action could be observed. Specific basolateral binding affinity of PAH was reduced to 50% of control. Furthermore, incubation with OTA led to
a decrease of PAH efflux across the apical membrane, although efflux
across the basolateral membrane and the amount remaining in the cells
increased as compared to control. By contrast to control cells, uptake
of PAH in OTA-treated cells was not stimulated after preloading with
glutarate. Our data show, that 1) long-term incubation with free OTA in
the nanomolar range reduces the activity of the organic anion
transporter, 2) without influencing general cell function. 3) OTA seems
to act preferentially on organic anion transport, by affecting the
exchange of organic anions and dicarboxylates. 4) Thereby, OTA
reduces its own secretion. 5) The excretion of other xenobiotics and
drugs may be also impaired, whereby OTA can exert an indirect toxic
action.
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