Scherer E Q, Wonneberger K, Wangemann P
Cell Physiology Laboratory, Kansas State University, 1600 Dension Ave, Manhattan, KS 66506, USA.
J Membr Biol. 2001 Aug 1;182(3):183-91. doi: 10.1007/s00232-001-0041-1.
Endothelins are known to be among the most potent endogenous vasoconstrictors. Vasoconstriction of the spiral modiolar artery, which supplies the cochlea, may be implicated in hearing loss and tinnitus. The purpose of the present study was to determine whether the spiral modiolar artery responds to endothelin, whether a change in the cytosolic Ca2+ concentration ([Ca2+]i) mediates the response and which endothelin receptors are present. The vascular diameter and [Ca2+]i were measured simultaneously by videomicroscopy and microfluorometry in the isolated spiral modiolar artery from the gerbil. ET-1 induced a transient [Ca2+]i increase and a strong and long-lasting vasoconstriction. The transient [Ca2+]i increase underwent rapid desensitization, was independent of extracellular Ca2+ and inhibited by the IP3-receptor blocker (75 microm) 2-aminoethoxydiphenyl borate (2-APB) and by depletion of Ca2+ stores with 10(-6) m thapsigargin. In contrast, the vasoconstriction displayed no comparable desensitization. The initial vasoconstriction was independent of extracellular Ca2+ but maintenance of the constriction depended on the presence of extracellular Ca2+. The half-maximal concentration values (EC50) for the agonists ET-1, ET-3 and sarafotoxin S6c were 0.8 nm, >10 nm and >100 nm, respectively. Affinity constants for the antagonists BQ-123 and BQ-788 were 24 nm and 77 nm, respectively. These observations demonstrate that ET-1 mediates a vasoconstriction of the gerbil spiral modiolar artery via ETA receptors and an IP3 receptor-mediated release of Ca2+ from thapsigargin-sensitive Ca2+ stores. The marked difference in desensitization between Ca2+ mobilization and vasoconstriction suggests that Ca2+ mobilization is not solely responsible for the vasoconstriction and that other signaling mechanisms must be present.
内皮素是已知最强效的内源性血管收缩剂之一。供应耳蜗的螺旋蜗轴动脉的血管收缩可能与听力损失和耳鸣有关。本研究的目的是确定螺旋蜗轴动脉是否对内皮素产生反应，胞质钙浓度（[Ca2+]i）的变化是否介导该反应，以及存在哪些内皮素受体。通过视频显微镜和微量荧光测定法同时测量来自沙鼠的离体螺旋蜗轴动脉的血管直径和[Ca2+]i。ET-1诱导[Ca2+]i短暂升高以及强烈且持久的血管收缩。[Ca2+]i的短暂升高迅速脱敏，不依赖细胞外钙，并被IP3受体阻滞剂（75微摩尔）2-氨基乙氧基二苯硼酸（2-APB）以及用10(-6)摩尔毒胡萝卜素耗尽钙库所抑制。相比之下，血管收缩没有表现出类似的脱敏现象。最初的血管收缩不依赖细胞外钙，但收缩的维持依赖于细胞外钙的存在。激动剂ET-1、ET-3和蛙皮毒素S6c的半数最大浓度值（EC50）分别为0.8纳米、>10纳米和>100纳米。拮抗剂BQ-123和BQ-788的亲和常数分别为24纳米和77纳米。这些观察结果表明，ET-1通过ETA受体和IP3受体介导的从毒胡萝卜素敏感的钙库中释放钙来介导沙鼠螺旋蜗轴动脉的血管收缩。钙动员和血管收缩之间脱敏的显著差异表明，钙动员并非血管收缩的唯一原因，必定还存在其他信号传导机制。
