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

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.