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

H2O2-induced pulmonary arterial smooth muscle (PASM) contractions are indep endent of Ca2+ and myosin light chain phosphorylation. The purpose of this study was to determine whether mitogen-activated protein kinase (MAPK), ext racellular signal-regulated kinase (ERK) 1 and ERK2, or protein kinase C (P KC) activation is required for H2O2-induced contraction. Porcine PASM strip s were stimulated with 1 mM H2O2, 120 mM KCl, or 10 mu M phorbol myristic a cetate and freeze clamped at various times during the contractions. Changes in relative amounts of tyrosine/threonine phosphorylated MAPK compared wit h total MAPK were measured. MAPK tyrosine phosphorylation levels increased in correlation with tension development. However, 50 mu M 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 b uffer containing P-32 and CaCl2 to measure the total myelin basic protein p hosphorylation. The data show that: 1) the time courses of PKC activity and force produced in response to H2O2 do not correlate, and 2) MAPK activatio n may be a concurrent event with, or a consequence of, tension development in response to a variety of agonists but is not responsible for contraction s to H2O2, high K+, or phorbol esters.