The mechanism of the increase of tonic tension produced by caffeine in sheep cardiac Purkinje fibres.
The mechanism of the increase of tonic tension produced by caffeine in sheep cardiac Purkinje fibres.
复制标题
咖啡因增加绵羊心脏浦肯野纤维强直张力的机制。
DOI：
10.1113/jphysiol.1985.sp015747
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发表时间：
1985
期刊：
影响因子：
--
通讯作者：
Valdeolmillos,M
中科院分区：
文献类型：
--
作者：
Eisner,DA;Valdeolmillos,M
研究了咖啡因对电压钳制的绵羊心脏浦肯野纤维的收缩和膜电流的影响。将发光蛋白水母发光蛋白注射到多个细胞中以测量细胞内离子化 Ca 浓度 [(Ca2+]i)。当Na-K泵受到抑制时，去极化会产生抽搐，然后产生紧张的紧张成分。复极产生后收缩。这些张力成分伴随着水母发光蛋白光的相应增加。咖啡因 (10 mM) 减少抽搐和后收缩，同时增加强直成分。咖啡因的应用还产生了水母发光蛋白光的短暂增加，无论是在去偏振期间还是在静止状态下，随后光信号的所有三个分量持续减少。特别是，尽管咖啡因在长时间去极化过程中降低了水母发光蛋白光的上升，但它却增加了强直张力。由于以下原因，咖啡因对强直张力的影响可能是由于抑制自发 Ca 振荡所致的可能性被拒绝。 (i) Ryanodine（也消除 Ca 振荡）降低了强直张力的强度。 (ii) 当将咖啡因添加到暴露于兰尼碱（1-10 微摩尔）的纤维中时，咖啡因仍然会增加张力。在兰尼碱存在的情况下，可以测量 [Ca2+]i 和紧张张力，而不受 Ca 振荡的干扰。咖啡因产生的强直张力的增加不能用[Ca2+]i 的增加来解释。结果表明，在一定的钙水平下，咖啡因会增加紧张感。结果表明，咖啡因产生的强直张力的增加很大一部分是由于收缩器官的Ca敏感性增加而不是[Ca2+]i的变化。讨论了咖啡因实验使用的这一观察结果。
The effects of caffeine were examined on contraction and membrane current in voltage‐clamped sheep cardiac Purkinje fibres. The photoprotein aequorin was injected into several cells in order to measure the intracellular ionized Ca concentration [( Ca2+]i). When the Na‐K pump was inhibited, depolarization produced a twitch followed by a tonic component of tension. Repolarization produced an after‐contraction. These components of tension were accompanied by corresponding increases of aequorin light. Caffeine (10 mM) decreased both the twitch and the after‐contraction while increasing the tonic component. The application of caffeine also produced a transient increase of aequorin light, both during depolarization and at rest, which was followed by a maintained decrease in all three components of the light signal. In particular, although caffeine decreased the rise of aequorin light during prolonged depolarization it increased the tonic tension. The possibility that the effects of caffeine on tonic tension could be due to suppression of spontaneous Ca oscillations was rejected for the following reasons. (i) Ryanodine (which also abolishes Ca oscillations) decreased the magnitude of the tonic tension. (ii) Caffeine still increased tonic tension when it was added to a fibre exposed to ryanodine (1‐10 microM). In the presence of ryanodine it was possible to measure [Ca2+]i and tonic tension without interference from Ca oscillations. The increase of tonic tension produced by caffeine could not be accounted for by a rise of [Ca2+]i. The results showed that, at a given level of Ca, caffeine increased tension. The results show that a large part of the increase of tonic tension produced by caffeine is due to an increase of the Ca sensitivity of the contractile apparatus rather than to changes of [Ca2+]i. The consequence of this observation for the experimental use of caffeine is discussed.