H2O2 mediates Ca2+- and MLC20 phosphorylation- independent contraction in intact and permeabilized vascular muscle

One purpose of the current study was to establish whether vasoconstriction occurs in all vessel types in response to H2O2. Isometric force was measure d in pulmonary venous and arterial rings, and isobaric contractions were me asured in mesenteric arteries and veins in response to H2O2. A second purpo se was to determine whether H2O2-induced contraction is calcium independent . The addition of H2O2 to calcium-depleted (using the Ca2+ ionophore ionomy cin in zero calcium EGTA buffer) muscle caused contraction. Furthermore, pe rmeabilized muscle contracted in response to H2O2 even in zero Ca2+. The fi nal purpose was to determine whether the 20-kDa regulatory myosin light cha in (MLC20) phosphorylation plays a role in H2O2-induced contraction. Pulmon ary arterial strips were freeze-clamped at various time points during H2O2- induced contractions, and the relative amounts of phosphorylated MLC20 were measured. H2O2 caused dose-dependent contractions that were independent of MLC20 phosphorylation. ML-9, a myosin light chain kinase inhibitor, had no effect on the H2O2 contractile response. In conclusion, H2O2 induces Ca2- and MLC20 phosphorylation-independent contraction in pulmonary and system ic arterial and venous smooth muscle.