ACTIVATION OF TYROSINE KINASES IN H2O2-INDUCED CONTRACTION IN PULMONARY-ARTERY

Hydrogen peroxide (H2O2) is an important reactive oxygen species impli cated in lung vascular constriction and injury. The purpose of this st udy was to investigate the role of tyrosine kinases in H2O2-induced va scular contraction and dysfunction. In our study, H2O2 (200 mu M) caus ed an initial transient contraction followed by a strong, sustained co ntraction in isolated rat pulmonary arteries. Genistein, a tyrosine ki nase inhibitor, attenuated both the initial and the sustained contract ions. Aminogenistein and tyrphostin 51, specific inhibitors of tyrosin e kinases, had the same effects as genistein. Exposure of pulmonary ar teries to H2O2 for 1 h caused a significant reduction in the contracti le response to KCl or phenylephrine and in the vasodilatory response t o acetylcholine (smooth muscle dysfunction). Although tyrosine kinase inhibitors significantly blocked contractions induced by H2O2, pretrea tment of pulmonary arteries with these inhibitors before H2O2 exposure did not prevent the decreases in responses to KCl, phenylephrine, or acetylcholine. Removal of extracellular Ca2+ and depletion of intracel lular Ca2+ pools by ryanodine or thapsigargin did not inhibit the init ial and sustained contractions in response to H2O2. W-7, a calmodulin antagonist, or ML-9, a myosin light chain kinase inhibitor, significan tly inhibited the sustained contractions but did not prevent smooth mu scle dysfunction induced by H2O2. These data show that 1) exposure to H2O2 causes smooth muscle contractions and dysfunction in isolated pul monary arteries and 2) activation of tyrosine kinases mediates H2O2-in duced contractions; however, tyrosine kinases do not appear to be invo lved in H2O2-induced inhibition of arterial responses to vasoactive su bstances. These data suggest that different signaling pathways and mec hanisms are involved in H2O2-induced smooth muscle contraction and dys function.