Regulation of smooth muscle contraction through remodeling of actin filaments

为了阐明2-氨基-4,4 a-二氢-4 a-7-二甲基- 3h -phenoxazine-3-one （Phx-1）对平滑肌制剂的松弛作用机制，我们研究了Phx-1对豚鼠盲肠完整和剥皮（细胞膜透化）制剂的收缩作用。在完整的制剂中，Phx-1浓度依赖性地抑制乙酰胆碱（ACh）或高k +诱导的收缩，IC50值估计在100 pM左右。Phx-1对力的类似抑制作用在细胞内钙储存耗尽的制剂中观察到。然而，在没有细胞外Ca的细胞膜去极化制剂中，Phx-1对咖啡因或乙酰胆碱诱导的收缩几乎没有影响。在剥皮制剂中，Phx-1在浓度高于100 μM时抑制Ca^<2+->诱导的收缩。这些结果表明，Phx-1似乎对肌动蛋白丝的组织有直接的抑制作用，尽管Phx-1对Ca^<2+>-内流的抑制作用要强得多。我们研究了强效肌球蛋白II抑制剂blebbistatin对β - escin剥皮盲肠带绦虫力学和结构特性的影响。Blebbistatin抑制Ca^<2+>诱导的收缩，仅对Ca^<2+>对力的敏感性有很小的影响，并且30mm Mg^<2+>诱导的力的发展，不依赖于肌球蛋白磷酸化。此外，Blebbistatin通过去除Ca^<2+>而加速松弛。上述blebbiatin效应的IC_<50>值接近25 μ m，表明blebbiatin直接作用于交叉桥相互作用。此外，blebbistatin抑制肌动蛋白和肌球蛋白丝的组织。由于blebbistatin不直接与肌动蛋白结合，肌凝蛋白丝的破坏似乎可以调节肌动蛋白丝的组织。少

1)Mechanism of the inhibitory effects of Phx-1 on the smooth muscle contraction To elucidate the mechanisms of relaxing effect of 2-amino-4,4 a-dihydro-4 a-7-dimethyl-3H-phenoxazine-3-one (Phx-1) on the smooth muscle preparations, we investigated effects of Phx-1 on the contraction of both intact and skinned (cell membrane peremeabilized) preparations from guinea pig tenia cecum. In intact preparations, Phx-1 concentration-dependently suppressed the contraction induced by either acetycholine(ACh) or high-K+ with the IC50 value estimated at around 100 pM. Similar inhibitory actions of Phx-1 on force were observed in intracellular Ca store depleted preparations. In the cell membrane depolarized preparations in the absence of extracellular Ca, however, Phx-1 had little effects on the caffeine-or ACh-induced contraction. In skinned preparations, Phx-1 suppressed the Ca^<2+->induced contraction at concentrations higher than 100 μM. These results suggest that Phx-1 seems to have direct inhib … More itory effect on the actin filaments organization, although inhibitory effect, of the Phx-1 on the Ca^<2+>-influx is much stronger.2)Contractile filaments remodeling by blebbistatin, a potent inhibitor of myosin II We studied the effects of blebbistatin, a potent inhibitor of myosin II on the mechanical and structural properties of beta escin skinned taenia cecum. Blebbistatin inhibited both Ca^<2+> induced contraction with only little effects on the Ca^<2+> sensitivity for the force, and 30 mM Mg^<2+> induced, myosin phosphorylation independent, force development, Also, blebbistatin accelerated relaxation by Ca^<2+> removal. IC_<50> values of the blebbistatin effects presented above were nearly 25 micro M. The present results suggested that blebbistain directly interfare cross-bridge interaction. Furthermore, blebbistatin inhibited organization of actin-and myosin-filaments. Since blebbistatin did not bind to actin directly, disruption of myosin filaments seemed to modulate actin filaments organization. Less