ACTION OF PROTEIN-KINASE-C IN ENDOTHELIN-INDUCED CONTRACTIONS IN RAT AORTIC RINGS

Endothelin (ET) is a potent vasoconstrictor peptide that induces chara cteristically long-lasting contractions. We used both intact and endot helium-denuded rat aortic rings to investigate the role of protein kin ase C (PKC) in ET-induced contractions. ET (10(-9) M) and phorbol 12,1 3-dibutyrate (PDBu), a PKC activator, produced a gradual and sustained contraction of greater magnitude in denuded aortic rings than in inta ct rings. When aortic rings were pretreated with graded concentrations of different PKC inhibitors, inhibition of ET-induced contractions be gan at 10(-9) M and was nearly complete at 10(-3) M, and the reduction was greater in intact than in denuded rings. Pretreatment of aortic r ings with PDBu or N-G-nitro-L-arginine methyl ester (L-NAME), an inhib itor of nitric oxide synthase, potentiated ET-induced contractions. PK C enzyme assay showed activation of PKC in aortic rings that were trea ted with either ET or PDBu, inhibition after pretreatment with PKC inh ibitors, and no change with 4 alpha-phorbol 12,13-didecanoate (PDD), a n inactive phorbol ester. ET significantly increased nitrate and nitri te production, which was further increased by pretreatment with PKC in hibitors. PDBu prevented ET-induced nitrate/nitrite production, and PD D had no effect. These results strongly suggest that PKC mediates, in part, ET-induced contractions in rat aortic rings and that an intact e ndothelium is required for maximum inhibition by PKC inhibitors becaus e PKC stimulated by ET inhibits nitric oxide release.