Abstract-We investigated whether the diminished contractile responsiveness to endothelin-1 (ET-1) is associated with the altered activation of mitogen-activated protein kinase (MAPK) in aortic smooth muscles from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. ET-1 dose-dependently increased contractions in aortic smooth muscle strips, and the contractions were significantly attenuated in tissues from DOCA-salt hypertensive rats compared with those from sham-operated rats. The phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 was elevated by ET-1, with the magnitude and time-course being similar between strips. Although ET-1 also increased the phosphorylation of p38 MAPK in both strips, the increment was markedly lower in the strips from DOCA-salt hypertensive rats compared with sham-operated controls. 5-Hydroxytryptamine (5-HT) increased vascular contraction and phosphorylation of both MAPK isoforms; these were greater in DOCA-salt hypertensive rats than in sham-operated rats. ET-1 also increased the phosphorylation of caldesmon, an actin-binding protein, in sham-operated and DOCA-salt hypertensive rats. However, the increment was markedly lower in the strips from DOCA-salt hypertensive rats compared with sham-operated controls. The phosphorylation of MAPK isoforms and caldesmon elevated by ET-1 was inhibited by PD098059, an inhibitor of ERK1/2 kinase, and SB203580, an inhibitor of p38 MAPK, respectively. These results suggest that ET-1 and 5-HT induce contraction by activating the MAPK pathway in rat aortic smooth muscle and that the diminished responsiveness to ET-1 in the DOCA-salt hypertensive rat may be, in part, mediated by the decrease of caldesmon phosphorylation after the decreased activation of p38 MAPK. 3,4 Previous reports have shown that ET-1 induces a sustained contraction, which results from the increase of [Ca 2ϩ ] i in isolated vascular smooth muscle. 5,6 In addition to the [Ca 2ϩ ] i -MLC kinase pathway, a number of intracellular signal molecules, including mitogen-activated protein kinase (MAPK), protein kinase C (PKC), phosphatidylinositol 3 kinase (PI3K), and Rho kinase, play important roles in the regulation of smooth muscle contraction. 4,7-10 ET-1 can also stimulate these kinases.MAPK is a family of serine/threonine-specific protein kinase, consisting of three isoforms: extracellular signalregulated kinase (ERK) 1/2, p38 MAPK, and stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK). 11,12 MAPK plays a central role in intracellular signal transduction initiated by extracellular stimuli, including growth factors, neurotransmitters, and hormones. 13,14 ERK1/2 is activated by receptor agonists, including angiotensin II and phenylephrine, which induce smooth muscle contraction. 15,16 ET-1 also increases the activity of ERK1/2 in vascular smooth muscle. [17][18][19] There is accumulating evidence that the MAPK pathway is closely linked to modulating the intensity of contraction in vascular smooth muscle. 15,20 -23 Moreover, the inhibition of p...

This study was designed to investigate the mechanism of endothelin-1 (ET-1) contractions in Staphylococcus alpha-toxin-permeabilized vascular smooth muscle. Rabbit small mesenteric arteries permeabilized with alpha-toxin were mounted for isometric or isotonic force recording or were processed for determination of myosin light chain (MLC) phosphorylation levels. Addition of 100 nM ET-1 plus 10 microM GTP significantly enhanced myofilament Ca2+ sensitivity as compared with the addition of Ca2+ alone (EC50, 0.47 microM Ca2+ for Ca2+ alone and 0.13 microM Ca2+ for ET-1 plus (GTP). This enhanced sensitivity was reversed by GDP beta S. ET-1-induced contractions were relaxed at a constant [Ca2+] by the addition of 30 microM cAMP or cGMP, demonstrating a direct effect of the cyclic nucleotides on contractile regulation. Inhibition of protein kinase C activity by 100 nM staurosporine relaxed ET-1 plus GTP-induced contractions, and pretreatment with 40 microM chelerythrine inhibited the ET-1 plus GTP increase in force. At 0.32 microM Ca2+, steady-state levels of shortening velocity were not increased by ET-1 plus GTP, although steady-state levels of MLC phosphorylation were significantly enhanced. The ET-1-induced increase in MLC phosphorylation was not altered by changes in [Ca2+], whereas the shortening velocity was Ca2+ dependent, suggesting that the increase MLC phosphorylation level may be the result of protein kinase C, rather than MLC kinase, activation. These results are consistent with the hypothesis that ET-1 increases myofilament Ca2+ sensitivity by a G protein-dependent pathway and subsequent activation of protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)

Epigallocatechin-3-O-gallate (EGCG) is the main catechin, which is derived from Camellia sinensis plant. Vascular cell adhesion molecules (VCAMs) and intercellular adhesion molecules (ICAMs) mediate the binding of inflammatory cells onto the vascular wall-promoting the early phase of atherosclerosis. In the present study, we investigated the mechanism(s) by which EGCG inhibits angiotensin II (Ang II)-induced elevation of the membrane associated VCAM-1 and ICAM-1 in human umbilical vein endothelial cells (HUVEC). Ang II induced a 40% increase of VCAM-1 and ICAM-1 in the plasma membrane. EGCG (10 to 50 µM) inhibited the effect of Ang II in a concentration-dependent manner. In parallel, the Ang II-induced elevation of the mRNA expressions of VCAM-1 and ICAM-1 in HUVEC were completely inhibited by 50 µM EGCG. Since mitogen-activated protein kinase (MAPK) families are involved in vascular inflammation in response to stressful stimuli, we investigated the effects of EGCG on the MAPK signal transduction pathway stimulated by Ang II. EGCG (30 to 50 µM) completely inhibited the Ang II-induced phosphorylation of ERK (extracellular signal-regulated kinase) 1/2 and p38 MAPK. PD98059, an inhibitor of ERK1/2 inhibited the Ang II-induced increase of VCAM-1 but not of ICAM-1 in the plasma membranes. In contrast, SB203580, an inhibitor of p38 MAPK inhibited both the Ang II-induced enrichment of ICAM-1 and VCAM-1. From these results, it may be concluded that EGCG inhibits the Ang II-induced elevation of VCAM-1 and ICAM-1 in the HUVEC plasma membranes via inhibition of the p38 MAPK and the ERK1/2 signalling pathways resulting in an inhibition of the VCAM-1 and ICAM-1 transcription.