Endothelin ET(A) receptor regulates signaling and ANF gene expression via multiple G protein-linked pathways

We have characterized the interaction of endothelin (ET) with cultured neonatal rat ventricular myocytes. Binding studies indicate a single population of ET(A) receptors [53,000 sites/cell, apparent dissociation constant (K(d)) for ET-1 = 0.07 nM]. Analysis of mRNA levels for ET receptors using 35 cycles of reverse transcriptase-polymerase chain reaction demonstrates the presence of only ET(A)-receptor message. Studies with ET-1 and a variety of congeners and antagonists indicate that ET(A) receptors couple to both the stimulation of phosphoinositide turnover and the inhibition of adenylyl cyclase. In myocytes transfected with an atrial natriuretic factor (ANF) promoter linked to a luciferase reporter gone, ET-1 stimulates luciferase expression through an ET(A) receptor. These data indicate that the ETA receptor is the exclusive receptor on neonatal ventricular myocytes and that this receptor couples to both phosphoinositide hydrolysis and adenylyl cyclase. ET-1 also induces a threefold increase in mitogen-activated protein kinase (MAPK) activity, an effect that is not sensitive to pertussis toxin (PTx). By contrast, ET-stimulated ANF-luciferase expression is partially inhibited by treatment of cells with PTx, suggesting that both PTx-sensitive (G(i)) and PTx-insensitive (G(q)) pathways mediate the effects of ET-1 on ANF gene expression in neonatal myocytes and that hormonal regulation of ANF express on may utilize pathways in addition to the activation of MAPK.