MAPK and PKC activity are not required for H2O2-induced arterial muscle contraction

1 Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120; 2 Department of Biochemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6; and 3 Department of Internal Medicine, Pulmonary Division, University of Cincinnati, Cincinnati, Ohio 45267-0564 H 2 O 2 -induced pulmonary arterial smooth muscle (PASM) contractions are independent of Ca 2+ and myosin light chain phosphorylation. The purpose of this study was to determine whether mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK) 1 and ERK2, or protein kinase C (PKC) activation is required for H 2 O 2 -induced contraction. Porcine PASM strips were stimulated with 1 mM H 2 O 2 , 120 mM KCl, or 10 µM phorbol myristic acetate and freeze clamped at various times during the contractions. Changes in relative amounts of tyrosine/threonine phosphorylated MAPK compared with total MAPK were measured. MAPK tyrosine phosphorylation levels increased in correlation with tension development. However, 50 µM PD-98059, a MAPK/ERK kinase-MAPK kinase blocker, reduced MAPK phosphorylation below resting levels, even though the magnitude of the isometric tension development was unaltered. Freeze-clamped PASM strips were placed in a PKC activity assay buffer containing 32 P and CaCl 2 to measure the total myelin basic protein phosphorylation. The data show that: 1 ) the time courses of PKC activity and force produced in response to H 2 O 2 do not correlate, and 2 ) MAPK activation may be a concurrent event with, or a consequence of, tension development in response to a variety of agonists but is not responsible for contractions to H 2 O 2 , high K + , or phorbol esters. reactive oxygen species; vasoconstriction; second messengers; mitogen-activated protein kinase; protein kinase C