Instituto de Biomedicina de Sevilla, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Sevilla, Spain.
Circ Res. 2011 May 27;108(11):1348-57. doi: 10.1161/CIRCRESAHA.111.240127. Epub 2011 Apr 14.
Sustained vascular smooth muscle contraction is mediated by extracellular Ca(2+) influx through L-type voltage-gated Ca(2+) channels (VGCC) and RhoA/Rho-associated kinase (ROCK)-dependent Ca(2+) sensitization of the contractile machinery. VGCC activation can also trigger an ion-independent metabotropic pathway that involves G-protein/phospholipase C activation, inositol 1,4,5-trisphosphate synthesis, and Ca(2+) release from the sarcoplasmic reticulum (calcium channel-induced Ca(2+) release). We have studied the functional role of calcium channel-induced Ca(2+) release and the inter-relations between Ca(2+) channel and RhoA/ROCK activation.
We have used normal and genetically modified animals to study single myocyte electrophysiology and fluorimetry as well as cytosolic Ca(2+) and diameter in intact arteries. These analyses were complemented with measurement of tension and RhoA activity in normal and reversibly permeabilized arterial rings. We have found that, unexpectedly, L-type Ca(2+) channel activation and subsequent metabotropic Ca(2+) release from sarcoplasmic reticulum participate in depolarization-evoked RhoA/ROCK activity and sustained arterial contraction. We show that these phenomena do not depend on the change in the membrane potential itself, or the mere release of Ca(2+) from the sarcoplasmic reticulum, but they require the simultaneous activation of VGCC and the downstream metabotropic pathway with concomitant Ca(2+) release. During protracted depolarizations, refilling of the stores by a residual extracellular Ca(2+) influx through VGCC helps maintaining RhoA activity and sustained arterial contraction.
These findings reveal that calcium channel-induced Ca(2+) release has a major role in tonic vascular smooth muscle contractility because it links membrane depolarization and Ca(2+) channel activation with metabotropic Ca(2+) release and sensitization (RhoA/ROCK stimulation).
持续的血管平滑肌收缩是通过 L 型电压门控钙通道（VGCC）介导的细胞外 Ca2+内流和 RhoA/Rho 相关激酶（ROCK）依赖性收缩机制的 Ca2+敏感化来实现的。VGCC 的激活还可以触发一种离子非依赖性代谢途径，该途径涉及 G 蛋白/磷脂酶 C 的激活、肌醇 1,4,5-三磷酸的合成以及肌浆网（钙通道诱导的 Ca2+释放）中 Ca2+的释放。我们研究了钙通道诱导的 Ca2+释放的功能作用以及钙通道与 RhoA/ROCK 激活之间的相互关系。
我们使用正常和基因修饰的动物来研究单个心肌细胞的电生理学和荧光法以及完整动脉中的胞质 Ca2+和直径。这些分析与正常和可逆通透动脉环中张力和 RhoA 活性的测量相结合。我们发现，出乎意料的是，L 型 Ca2+通道的激活以及随后肌浆网中代谢性 Ca2+的释放，参与了去极化引发的 RhoA/ROCK 活性和持续的动脉收缩。我们表明，这些现象不依赖于膜电位本身的变化，或者肌浆网中 Ca2+的单纯释放，而是需要 VGCC 的同时激活以及下游代谢途径的同时激活，伴随着 Ca2+的释放。在长时间的去极化过程中，通过 VGCC 进入细胞外的残留 Ca2+内流来补充储存库，有助于维持 RhoA 活性和持续的动脉收缩。
这些发现表明，钙通道诱导的 Ca2+释放在血管平滑肌紧张性收缩中起着重要作用，因为它将膜去极化和 Ca2+通道激活与代谢性 Ca2+释放和敏感性（RhoA/ROCK 刺激）联系起来。
