A CAFFEINE-SENSITIVE AND RYANODINE-SENSITIVE CA2+ STORE IN BULLFROG SYMPATHETIC NEURONS MODULATES EFFECTS OF CA2+ ENTRY ON [CA2+]I
A CAFFEINE-SENSITIVE AND RYANODINE-SENSITIVE CA2+ STORE IN BULLFROG SYMPATHETIC NEURONS MODULATES EFFECTS OF CA2+ ENTRY ON [CA2+]I
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DOI：
10.1113/jphysiol.1992.sp019125
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发表时间：
1992-05-01
影响因子：
5.5
通讯作者：
TSIEN, RW
中科院分区：
文献类型：
--
作者：
FRIEL, DD;TSIEN, RW
1.我们研究了牛蛙交感神经元中咖啡因敏感的Ca 2+储存如何影响电压依赖性Ca 2+内流产生的胞浆游离Ca 2+浓度（[Ca 2 +]i）的变化。通过K+去极化引起Ca 2+内流，并用咖啡因或ryanodine操纵钙库.在释放咖啡因储存并切换到无咖啡因培养基后的一段时间内：（a）[Ca 2 +]i被抑制至低于静息水平40-50 nM，（B）咖啡因反应性减弱，（c）短暂的K+应用引起[Ca 2 +]i反应，与对照组相比，起效较慢，恢复较快。这些效果更明显的条件咖啡因浓度增加超过1-30 mM的范围。3. [Ca2+]i，咖啡因和K+反应性平行恢复，半衰期约为2 min。恢复需要外部Ca 2+，并通过增加胞浆Ca 2+的可用性来加速，这表明它反映了以胞浆Ca 2+为代价的储存补充。在恢复过程中，去极化刺激的Ca 2+内流对[Ca 2 +]i的影响最小时，商店是最迅速的填充。这表明Ca 2+进入对[Ca 2 +]i的影响被改变，至少部分是因为在刺激期间进入胞质溶胶的一些Ca 2+在其重新填充时被储存所吸收。进行进一步的实验以研究是否商店也可以响应于刺激的Ca 2+进入而释放Ca 2+。在低浓度（1 mM）咖啡因的持续存在下，与对照组相比，高K+引起更快和更大的[Ca 2 +]i反应;在较高浓度的咖啡因（10和30 mM）下，反应被抑制。Ryanodine（1 μ M）降低了[Ca 2 +]i随Ca 2+进入而增加的速率，但未达到释放储存后观察到的程度。在此浓度下，ryanodine完全阻断对咖啡因的反应，但对Ca 2+通道电流或去极化期间达到的稳定[Ca 2 +]i水平没有可检测的影响。我们建议，根据其Ca 2+含量，咖啡因敏感的存储可以减弱或增强去极化反应。当耗尽和在再填充的过程中，存储减少的影响，Ca 2+进入的一些Ca 2+在刺激期间进入胞质溶胶被捕获的存储。当充满时，钙库通过释放Ca 2+（可能是通过Ca 2+诱导的Ca 2+释放）来放大Ca 2+进入的效果，这一作用在低浓度时被咖啡因增强;通过阻止钙库和细胞质之间的净Ca 2+交换，ryanodine消除了这两种作用。8.活动依赖性的变化，在钙含量的咖啡因敏感的商店，或调节其Ca 2+转运活动，可以显着影响背景[Ca 2 +]i和刺激诱发的变化[Ca 2 +]i。
1. We studied how in changes in cytosolic free Ca2+ concentration ([Ca2+]i) produced by voltage-dependent Ca2+ entry are influenced by a caffeine-sensitive Ca2+ store in bullfrog sympathetic neurones. Ca2+ influx was elicited by K+ depolarization and the store was manipulated with either caffeine or ryanodine.2. For a time after discharging the store with caffeine and switching to a caffeine-free medium: (a) [Ca2+]i was depressed by up to 40-50 nM below the resting level, (b) caffeine responsiveness was diminished, and (c) brief K+ applications elicited [Ca2+]i responses with slower onset and faster recovery than controls. These effects were more pronounced as the conditioning caffeine concentration was increased over the range 1-30 mM.3. [Ca2+]i, caffeine and K+ responsiveness recovered in parallel with a half-time of approximately 2 min. Recovery required external Ca2+ and was speeded by increasing the availability of cytosolic Ca2+, suggesting that it reflected replenishment of the store at the expense of cytosolic Ca2+.4. During recovery, Ca2+ entry stimulated by depolarization had the least effect on [Ca2+]i when the store was filling most rapidly. This suggests that the effect of Ca2+ entry on [Ca2+]i is modified, at least in part, because some of the Ca2+ which enters the cytosol during stimulation is taken up by the store as it refills.5. Further experiments were carried out to investigate whether the store can also release Ca2+ in response to stimulated Ca2+ entry. In the continued presence of caffeine at a low concentration (1 mM), high K+ elicited a faster and larger [Ca2+]i response compared to controls; at higher concentrations of caffeine (10 and 30 mM) responses were depressed.6. Ryanodine (1-mu-M) reduced the rate at which [Ca2+]i increased with Ca2+ entry, but not to the degree observed after discharging the store. At this concentration, ryanodine completely blocked responses to caffeine but had no detectable effect on Ca2+ channel current or the steady [Ca2+]i level achieved during depolarization.7. We propose that, depending on its Ca2+ content, the caffeine-sensitive store can either attenuate or potentiate responses to depolarization. When depleted and in the process of refilling, the store reduces the impact of Ca2+ entry as some of the Ca2+ entering the cytosol during stimulation is captured by the store. When full, the store amplifies the effects of Ca2+ entry by releasing Ca2+ (presumably via Ca2+-induced Ca2+ release), an action that is enhanced by caffeine at low concentration; by preventing net Ca2+ exchange between the store and cytosol, ryanodine abolishes both of these effects.8. Activity-dependent changes in the Ca2+ content of the caffeine-sensitive store, or regulation of its Ca2+ transport activity, could significantly influence both background [Ca2+]i and stimulus-evoked changes in [Ca2+]i.