Phosphorylation of endothelial myosin light chains (MLC) is a key mechanism in control of endothelial contractile machinery. Extracellular ATP influences endothelial MLC phosphorylation by either activation of Ca2+-dependent MLC kinase or Ca2+-independent MLC phosphatase. Here, the role of the MEK/MAPK pathway in this signaling was investigated in porcine aortic endothelial cells. Phosphorylation of ERK2 and phosphorylation of MLC were analyzed in cultured aortic endothelial cells. ATP (10 μM) increased ERK2 phosphorylation from basal 17 ± 3 to 53 ± 4%, an effect suppressed in the presence of the MEK inhibitors PD-98059 (20 μM) or U0126 (10 μM). Phosphorylation of ERK2 was not dependent on the ATP-induced cytosolic Ca2+ rise, because it was unaltered when this was suppressed by the Ca2+ chelator BAPTA (10 μM) or xestospongin C (3 μM), an inhibitor of the inositol 1,4,5-trisphosphate-sensitive Ca2+ release mechanism of the endoplasmic reticulum. Phosphorylation of ERK2 was neither induced by the adenosine analog 5′-( N-ethylcarboxamido)adenosine (1 μM) nor inhibited in the presence of the adenosine receptor antagonist 8-phenyltheophylline (10 μM). ATP increased MLC kinase activity, and this was blocked in presence of PD-98059. ATP also increased MLC phosphatase activity, which was not inhibited by PD-98059. The MEK/MAPK pathway is a Ca2+-independent part of ATP signaling toward MLC kinase but not of ATP signaling toward MLC phosphatase.
Role of c-Jun protein in thrombin- stimulated expression of preproendothelin-1 mRNA in porcine aortic endothelial cells.
