Uncoupling of force and myosin light chain phosphorylation produced by slow stretch in vascular smooth muscle.

研究了犬基底动脉缓慢拉伸收缩过程中肌球蛋白轻链（MLC）磷酸化与力的关系。在四乙基铵（5毫米）存在的情况下，在15分钟的刺激期间，以1毫米/秒的速度缓慢拉伸至初始肌肉长度的1.5倍，会产生多种磷酸化的MLC物种（至少是单磷酸化、二磷酸化和三磷酸化物种）的增加，而没有任何明显的收缩，表明力和MLC磷酸化的解耦。缓慢拉伸还增加了蛋白激酶C (PKC)-α和PKC-δ从细胞质向膜组分的易位。nicardipine（一种1,4-二氢吡啶Ca^<2+>通道阻滞剂）、ML-9（一种肌凝蛋白轻链激酶抑制剂）或calphostin C（一种cPKC/nPKC抑制剂）对MLC磷酸化的抑制作用约为未用药动脉的50%。Y-27632（一种rho激酶抑制剂）可消除MLC磷酸化。相比之下，rottlerin （5 μM， PKC-δ的假定抑制剂）对MLC磷酸化没有明显影响。PKC-α的易位仅被calphostin C抑制，PKC-δ的易位被calphostin C、Y-27632或rottlerin减弱。冈田酸（一种磷酸酶抑制剂）抑制80 mM kcl诱导的收缩，但增加了多个磷酸化的MLC物种。考虑到PKC-α和δ的易位对其激活至关重要，本研究结果表明，Rho/Rho激酶活性和PKC-δ以外的PKC参与了MLC的磷酸化而没有收缩。

Relationship between force and myosin light chain (MLC) phosphorylation in slow stretch-induced contraction in canine basilar artery was investigated. In the presence of tetraethyl-ammonium (5 mM), slow stretch at a rate of 1 mm/sec up to 1.5 times initial muscle length during a stimulus period of 15 min produced an increase in multiple phosphorylated MLC species (at least mono-, di- and tri-phosphorylated species) without any apparent contraction, indicating uncoupling of force and MLC phosphorylation. Slow stretch also increased translocation of protein kinase C (PKC)-α and PKC-δ from the cytosol to the membrane fraction. The MLC phosphorylation was inhibited by nicardipine (a 1,4-dihydropyridine Ca^<2+> channel blocker), ML-9 (an inhibitor of myosin light chain kinase) or calphostin C (a cPKC/nPKC inhibitor) to about 50% of that in drug-untreated artery. Y-27632 ( a Rho-kinase inhibitor) abolished the MLC phosphorylation. In contrast, rottlerin (5 μM, a putative inhibitor of PKC-δ) had no apparent effect on MLC phosphorylation. The translocation of PKC-α was inhibited by only calphostin C, and that of PKC-δ was attenuated by calphostin C, Y-27632 or rottlerin. Okadaic acid (an inhibitor of phosphatase) inhibited 80 mM KCl-induced contraction, but it increased multiple phosphorylated MLC species.Considering that the translocation of PKC-α and δ is important for their activation, the present results suggest that Rho/Rho-kinase activity and PKC other than PKC-δ are involved in MLC phosphorylation without contraction.