-dependent Pathway in OKP Cells

To examine the mechanisms by which endothelin (ET) regulates the Na/H antiporter isoform, NHE-3, OKP cells were stably transfected with ET A and ET B receptor cDNA. In cells overexpressing ET B , but not ET A receptors, ET-1 increased Na/H antiporter activity (J Na/H ). This effect was inhibited by a nonselective endothelin receptor blocker and by a selective ET B receptor blocker but was not inhibited by an ET A selective receptor blocker. In ET B -overexpressing cells, 10 2 8 M ET-1 inhibited adenylyl cyclase, but protein kinase A inhibition and pertussis toxin pretreatment did not affect Na/H antiporter activation by ET-1. ET-1 caused a transient increase in cell [Ca 2 1 ], followed by a sustained increase. Increases in cell [Ca 2 1 ] were partially inhibited by pertussis toxin. ET-1–induced increases in J Na/H were 50% inhibited by clamping cell [Ca 2 1 ] low with BAPTA, and by KN62, a Ca-calmodulin kinase inhibitor. Inhibitors of protein kinase C, cyclooxygenase, lipoxygenase, and cytochrome P450 and cyclic GMP were without effect. In ET A overexpressing cells, ET-1 increased cell [Ca 2 1 ] but did not increase J Na/H . In summary, binding of ET-1 to ET B receptors increases Na/H antiporter activity in OKP cells, an effect mediated in part by increases in cell [Ca 2 1 ] and Cacalmodulin kinase. Increases in cell [Ca 2 1 ] are not sufficient for Na/H antiporter activation. ( J. Clin. Invest. 1996. 97: 1454–1462.)