异搏定和钆对青蛙骨骼肌纤维中咖啡因诱导的痉挛和钙离子流的影响

许多研究证明咖啡因可以诱导骨骼肌的收缩，但Axelsson等科学家在青蛙的骨骼肌中注入咖啡因后却未发现收缩现象。面对这种现象，澳大利亚Tasmania大学的Lana Shabala等科学家推测咖啡因引起的青蛙慢骨骼肌纤维收缩的活性位点在胞外。

Lana Shabala等科学家采用 “非损伤微测技术（MIFE）”检测了Ca²⁺通道阻断剂异博定和钆预处理，再加入咖啡因后Ca²⁺净流量的变化情况，发现Ca²⁺净流量的变化与肌肉紧张度的变化相互依赖并且相互依存，同时发现Ca²⁺通道抑制剂钆的作用效果优于异博定。本项研究揭示：在慢肌肉纤维收缩的复杂机制中，L-型Ca²⁺通道首先发挥了触发器的作用，而随后的过程由正向的Ca²⁺诱导的Ca²⁺释放和胞浆去Ca²⁺化的负反馈回路两种途径来调解。

非损伤微测技术为该实验提供了动力学研究的平台，为进一步阐明Ca²⁺参与青蛙慢骨骼肌纤维的收缩提供了直接依据。

关键词：慢肌肉纤维(Slow muscle fiber)；咖啡因挛缩(Caffeine contracture)；钙离子流(Calcium flux)；异博定(Verapamil)；钆(Gadolinium)；非损伤微测技术(non-invasively using ion-selective vibrating microelectrodes， MIFE)。

参考文献：Lana Shabala, et al. J Membrane Biol, 2008, 221: 7–13

全文下载：http://www.xuyue.net/xylt/viewthread.php?tid=466&extra=page%3D1

Abstract：

In this work, we tested whether L-type Ca²⁺ channels are involved in the increase of caffeine-evoked tension in frog slow muscle fibers. Simultaneous net Ca²⁺ fluxes and changes in muscle tension were measured in the presence of caffeine. Isometric tension was recorded by a mechanoelectrical transducer, and net fluxes of Ca²⁺ were measured noninvasively using ion-selective vibrating microelectrodes. We show that the timing of changes in net fluxes and muscle tension coincided, suggesting interdependence of the two processes. The effects of Ca²⁺ channel blockers (verapamil and gadolinium) were explored using 6 mM caffeine; both significantly reduced the action of caffeine on tension and on calcium fluxes. Both caffeineevoked Ca²⁺ leak and muscle tension were reduced by 75% in the presence of 100 lM GdCl₃, which also caused a 92% inhibition of net Ca²⁺ fluxes in the steady-state condition. Application of 10 lM verapamil to the bath led to 30% and 52% reductions in the Ca²⁺ leak caused by the presence of caffeine for the peak and steady-state values of net Ca²⁺ fluxes, respectively. Verapamil (10 lM) caused a 30% reduction in the maximum values of caffeine-evoked muscle tension. Gd³⁺ was a more potent inhibitor than verapamil. In conclusion, L-type Ca²⁺ channels appear to play the initial role of trigger in the rather complex mechanism of slow fiber contraction, the latter process being mediated by both positive Ca²⁺-induced Ca²⁺ release and negative (Ca²⁺ removal from cytosol) feedback loops.