Ca2+/Calmodulin-Dependent and -Independent Mechanisms are Involved in Angiotension II-induced Contraction of Rat Aortic Smooth Muscle / 대한마취과학회지

ABSTRACT

BACKGROUND: Angiotensin II (Ang II) appears to play important roles in the pathogenesis of hypertension. However, the mechanism by which Ang II induces vascular smooth muscle contraction is not fully understood. The phosphorylation of myosin light chain (MLC) is an essential trigger of the cascade that initiates of smooth muscle contraction. In this study, we investigated the role of MLC phosphorylation on Ang II-induced vascular smooth muscle contraction. METHODS: Rat thoracic aortas were used as an experimental substrates. We measured isometric tension, myosin light chain phosphorylation, intracellular Ca2+ concentration, mitogen-activated protein kinase phosphorylation, and tyrosine phosphorylation. RESULTS: 100 nM Ang II increased smooth muscle contraction transiently in rat thoracic aorta. Ang II also increased intracellular Ca2+ and 20 kDa MLC phosphorylation. Pretreatment with 10microM verapamil and 30microM La3+ abolished the contraction developed at 30 seconds by Ang II, whereas pretreatment with 10microM verapamil and 30microM La3+ abolished the contraction and the intracellular Ca2+ increase induced at 2 minutes by Ang II. Moreover, pretreatment of 10microM verapamil, 30microM La3+ and 1microM thapsigargin abolished the contraction as well as intracellular Ca2+ increase developed at 30 seconds and 2 minutes by Ang II. However, MLC phosphorylation was not affected. GF109203X attenuated Ang II-induced contraction more so than ML-7. 100 nM Ang II increased tyrosine phosphorylation of mitogen-activated protein kinase, 68 and 125 kDa proteins. The 125 kDa protein was confirmed as paxillin in primary vascular smooth muscle cell culture. CONCLUSIONS: Ang II-induced contraction involves Ca2+-dependent and independent components, and Ca2+-dependent contraction by Ang II is mediated by voltage-dependent Ca2+ channel. Moreover, protein kinase C and the mitogen-activated protein kinase activation pathway are involved in Ang II-induced contraction.