Myoendothelial signal transmission through gap junctions in arterioles

用电子显微镜观察了豚鼠肠系膜小动脉(直径50~100μm)的切片，发现有单层的平滑肌细胞。典型的缝隙连接仅在内皮细胞之间容易观察到。连接蛋白40仅在血管内皮细胞膜上表达，而连接蛋白43在血管内皮细胞膜和血管内皮细胞膜上均有表达。注射到血管内皮细胞的神经生物素扩散到邻近的几个血管内皮细胞中，而注射到内皮细胞中的神经生物素扩散到许多内皮细胞中。采用常规或穿孔全细胞钳制方法和视频边缘检测技术，观察外翻或去外膜小动脉的电活动和机械活动。内皮细胞之间连接良好。相邻平滑肌细胞之间的偶联阻力至少为90MΩ，一个平滑肌细胞与整个内皮层之间的偶联阻力为0.9GΩ。在对照条件下，小动脉节段保持一定的基础张力，因为当去除外部钙离子时，小动脉节段扩张。小动脉直径是随机波动的，这是由于小而局部的收缩没有伴随膜电位的波动。缝隙连接阻滞剂18β-甘草次酸使肌膜超极化，降低微动脉基础张力。由于高K~+溶液在18β-甘草次酸存在和不存在时引起相似的收缩，该物质似乎不干扰血管的收缩。当这两层与完整的肌-内皮细胞缝隙连接偶联时，内皮细胞可能使平滑肌膜去极化并产生基础张力。

Segments of guinea-pig mesenteric arterioles (diameter : 50 - 100 μm) have been investigated In electron micrographs preparations were found to have a single layer of smooth muscle cells. Typical gap junctions were readily observed between endothelial cells only. While immunoreactivity to connexin 40 was strongly expressed on the membranes of endothelial cells only, that to connexin 43 was expressed on both smooth muscle and endothelial cell membranes. Neurobiotin injected into smooth muscle cell diffused into several neighboring smooth muscle cells while that injected into an endothelial cell diffused into many endothelial cells. The diffusion between two layers could also be observed.Using the conventional or perforated whole-cell clamp method and the video-edge detection, the electrical and mechanical activities of the everted or adventitia-removed arterioles have been observed. The endothelial cells were well coupled to each other. The coupling resistance between adjacent smooth muscle cells was estimated to be at least 90 MΩ and that between a smooth muscle cell and the whole endothelial layer to be 0.9 GΩ.The arteriole segments maintained some basal tone under the control condition, since they dilated when the external Ca^<2+> was removed. The arteriolar diameter was randomly fluctuating due to small and local contractions which were not accompanied by the membrane potential fluctuations. A gap junction blocker 18 β-glycyrrhetinic acid hyperpolarized the smooth muscle membrane and decreased the arteriolar basal tone. As high K^+ solution induced comparable contractions in the absence and the presence of 18 β-glycyrrhetinic acid, this substance did not seem to interfere with the smooth muscle contractility. The endothelium might depolarize the smooth muscle membrane and induce the basal tone when these two layers are coupled with intact myoendothelial gap junctions.