Nephrotoxicants induce endothelin release and signaling in renal proximal tubules: Effect on drug efflux

We previously used killifish proximal tubules, fluorescent substrates, and confocal microscopy to demonstrate that transport mediated by the multidrug resistance protein (Mrp2) and by P-glycoprotein was reduced by nanomolar c oncentrations of endothelin-1 (ET), acting through a basolateral B-type ET receptor and protein kinase C (PKC). Here we show that representatives of t wo classes of nephrotoxicants decrease transport by activating the endothel in-PKC signaling pathway. Exposing tubules to radiocontrast agents (iohexol , diatrizoate) or aminoglycoside antibiotics (gentamicin, amikacin) reduced Mrp2-mediated fluorescein methotrexate (FL-M-DC) transport from cell to tu bular lumen. Pretreating the tubules with an ETB-receptor antagonist or wit h PKC-selective inhibitors abolished these effects. The nephrotoxicants act ivated signaling by inducing release of ET from the tubules, because adding of an antibody against ET to the medium abolished the effects. Elevating m edium Ca2+ also reduced FL-MTX transport; this reduction was abolished when tubules were pretreated with an ET antibody, an FTB-receptor antagonist, P KC-selective inhibitors, or the Ca2+ channel blocker, nifedipine. None of t hese drugs by themselves affected FL-MTX transport. Importantly, nifedipine also blocked the ETB-receptor/PKC-dependent reduction in FL-MTX transport caused by gentamicin and diatrizoate. These results for two classes of stru cturally unrelated nephrotoxicants suggest that Ca2+-dependent ET release a nd subsequent action through an autocrine mechanism may be an early respons e to tubular injury.