Department of Medical Pharmacology and Toxicology, and Microcirculation Research Institute, College of Medicine, Texas A&M University, College Station, TX 77843-1114, USA.
Acta Pharmacol Sin. 2010 Jan;31(1):19-26. doi: 10.1038/aps.2009.164. Epub 2009 Nov 16.
To quantitatively assess the effect of lowering external Ca(2+) (Ca(2+)) on both endothelium-dependent and -independent relaxations in rabbit aorta.
Isometric contractions and relaxations of isolated aortae were recorded. When assessing the effect of reduced Ca(2+) on relaxations, the normal Ca(2+) solution was substituted with one of the reduced Ca(2+) solutions for one aorta, while a paired aorta was replenished with normal Ca(2+) solution.
The extent of acetylcholine (ACh)-induced relaxation, which is dependent on an intact endothelium, is time-dependent, and inversely related to Ca(2+) in a range of 0.02-2 mmol/L. ACh-induced relaxations were not significantly altered by the magnitude of the precontraction induced by PGF(2alpha). Nitroprusside-induced relaxations, which are independent of the endothelium, are also attenuated by reduced Ca(2+). Relaxant responses to ACh were significantly more susceptible to reduced Ca(2+) than nitroprusside-induced relaxations. A maximally effective relaxing concentration of D600, an L-type Ca channel blocker methoxyverapamil, (10(-5) mol/L) attenuated ACh-induced relaxations, whereas nitroprusside-induced relaxations were unaffected by D600.
Thus, endothelium-dependent relaxation is more dependent on Ca(2+) than endothelium-independent relaxation, and it seems likely that Ca(2+) plays an important role not only in contractile processes, but also in relaxant processes as well.
定量评估降低细胞外钙离子浓度(Ca(2+))对兔主动脉内皮依赖性和非内皮依赖性舒张的影响。
记录离体主动脉的等长收缩和舒张反应。在评估降低Ca(2+)对舒张反应的影响时，用低钙溶液替换一个主动脉的正常Ca(2+)溶液，而配对的主动脉则用正常Ca(2+)溶液补充。
乙酰胆碱(ACh)诱导的舒张反应（依赖于完整的内皮细胞）是时间依赖性的，与 0.02-2mmol/L 范围内的Ca(2+)呈反比关系。PGF(2alpha)诱导的预收缩幅度对 ACh 诱导的舒张反应没有显著影响。与内皮无关的硝普钠诱导的舒张反应也被降低的Ca(2+)所减弱。ACh 诱导的舒张反应对降低的Ca(2+)的敏感性明显高于硝普钠诱导的舒张反应。一种最大有效浓度的 L 型钙通道阻滞剂 D600（10(-5)mol/L）可减弱 ACh 诱导的舒张反应，而 D600 对硝普钠诱导的舒张反应无影响。
因此，内皮依赖性舒张比内皮非依赖性舒张更依赖于Ca(2+)，似乎Ca(2+)不仅在收缩过程中而且在舒张过程中也起着重要作用。
