Endothelin B receptor-mediated regulation of ATP-driven drug secretion in renal proximal tubule

In the kidney, endothelins (ETs) are important regulators of blood flow, gl omerular hemodynamics, and sodium and water homeostasis. They have been imp licated in the pathophysiology of acute ischemic renal failure, nephrotoxic ity by cyclosporine, cisplatin and radiocontrast agents, and vascular rejec tion of kidney transplants. Here, we used intact killifish renal proximal t ubules, fluorescent substrates for Mrp2 (fluorescein-methotrexate, FL-MTX) and P-glycoprotein (a fluorescent CSA derivative, NBD-CSA), and confocal mi croscopy to reveal a new role for renal ET: regulation of ATP-driven drug t ransport in proximal tubule. Subnanomolar to nanomolar concentrations of ET -1 rapidly reduced the cell-to-tubular lumen transport of both fluorescent compounds. These effects were prevented by an ETB receptor antagonist but n ot by an ETA receptor antagonist. Immunostaining with an antibody to mammal ian ETB receptors showed specific localization to the basolateral membrane of the fish tubular epithelial cells. ET-1 effects on transport were blocke d by protein kinase C-selective inhibitors, implicating protein kinase C in ET-1 signaling. Finally, the nephrotoxic radiocontrast agent iohexol reduc ed cell-to-lumen FL-MTX and NBD-CSA transport, and these effects were aboli shed by an ETB receptor antagonist. These are the first results linking ET to the control of xenobiotic transport and the first demonstrating control of renal multidrug resistance-associated protein 2 and P-glycoprotein by a hormone.