Effects of @entity2644 on excitation-contraction coupling events in fast-twitch skeletal muscle fibres of the XXXX .

@entity3326 @entity141 @entity262 @entity5834 @entity2644 @entity35 @entity5579
1. Single mechanically skinned fibres from the @entity35 extensor digitorum longus muscle, which allow access to intracellular compartments, were used to examine the effects of 0.5-100 microM @entity2644 ( @entity5579 ) on the major steps of the excitation-contraction (E-C) coupling to elucidate the involvement of skeletal muscle in the @entity3326 ( @entity3326 ). 2. At 1 microM, @entity5579 caused a 20-30% increase in the force response induced by @entity262 and a marked increase in the rate of @entity5834 -induced SR @entity141 release. At [ @entity5579 ]> or =2.5 microM, there was an initial increase followed by a marked decrease of the @entity262 -induced force responses, while the potentiating effect on the @entity5834 -induced SR @entity141 release remained. These effects were reversible. 3. @entity5579 had no effect on the maximum @entity141 -activated force, but caused reversible, concentration-dependent increases in the @entity141 sensitivity of the contractile apparatus at [ @entity5579 ] > or =10 microM, with a 50% predicted shift of 0.11 pCa (-log [ @entity141 ]) units at 82.3 microM @entity5579 . 4. @entity5579 did not alter the rate of SR- @entity141 loading at 1 and 10 microM, but reversibly reduced it by approximately 40% at 100 microM by reducing the SR @entity141 pump. Nevertheless, the SR @entity141 content was greater when fibres became unresponsive to t-system-induced depolarisation in the presence than in the absence of 100 microM @entity5579 . 5. The results show that @entity5579 has concentration-dependent stimulatory and inhibitory effects on various steps of the E-C coupling, which can explain the involvement of skeletal muscle in @entity3326 and reconcile previous divergent data on @entity5579 effects on muscle.
