Department of Pharmacology, Center for Cardiovascular Research, University of Nevada, Reno School of Medicine, Reno, NV 89557, USA.
Department of Pharmacology, University of Vermont, Burlington, VT 05405, USA.
Sci Signal. 2017 Sep 19;10(497):eaan2694. doi: 10.1126/scisignal.aan2694.
Junctional membrane complexes facilitate excitation-contraction coupling in skeletal and cardiac muscle cells by forming subcellular invaginations that maintain close (≤20 nm) proximity of ryanodine receptors (RyRs) on the sarcoplasmic reticulum (SR) with voltage-dependent Ca channels in the plasma membrane. In fully differentiated smooth muscle cells, junctional membrane complexes occur as distributed sites of peripheral coupling. We investigated the role of the cytoskeleton in maintaining peripheral coupling and associated Ca signaling networks within native smooth muscle cells of mouse and rat cerebral arteries. Using live-cell confocal and superresolution microscopy, we found that the tight interactions between the SR and the plasma membrane in these cells relied on arching microtubule structures present at the periphery of smooth muscle cells and were independent of the actin cytoskeleton. Loss of peripheral coupling associated with microtubule depolymerization altered the spatiotemporal properties of localized Ca sparks generated by the release of Ca through type 2 RyRs (RyR2s) on the SR and decreased the number of sites of colocalization between RyR2s and large-conductance Ca-activated K (BK) channels. The reduced BK channel activity associated with the loss of SR-plasma membrane interactions was accompanied by increased pressure-induced constriction of cerebral resistance arteries. We conclude that microtubule structures maintain peripheral coupling in contractile smooth muscle cells, which is crucial for the regulation of contractility and cerebral vascular tone.
连接膜复合物通过形成亚细胞内陷，使肌浆网上的ryanodine 受体 (RyRs) 与质膜上电压依赖性 Ca 通道保持紧密（≤20nm）的临近，从而促进骨骼肌和心肌细胞的兴奋-收缩偶联。在完全分化的平滑肌细胞中，连接膜复合物作为周边偶联的分布位点出现。我们研究了细胞骨架在维持固有平滑肌细胞内周边偶联和相关 Ca 信号网络中的作用，这些平滑肌细胞来自于小鼠和大鼠脑动脉。使用活细胞共聚焦和超分辨率显微镜，我们发现这些细胞中 SR 与质膜之间的紧密相互作用依赖于存在于平滑肌细胞外周的弓形微管结构，而与肌动蛋白细胞骨架无关。与微管解聚相关的周边偶联丧失改变了通过 SR 上的 2 型 RyR（RyR2）释放 Ca 产生的局部 Ca 火花的时空特性，并减少了 RyR2 与大电导 Ca 激活 K（BK）通道之间共定位的位点数量。与 SR-质膜相互作用丧失相关的 BK 通道活性降低伴随着压力诱导的脑阻力血管收缩增加。我们的结论是，微管结构维持了收缩性平滑肌细胞中的周边偶联，这对于调节收缩性和脑血管张力至关重要。
