Dynamics of signaling between Ca(2+) sparks and Ca(2+)- activated K(+) channels studied with a novel image-based method for direct intracellular measurement of ryanodine receptor Ca(2+) current.
Dynamics of signaling between Ca(2+) sparks and Ca(2+)- activated K(+) channels studied with a novel image-based method for direct intracellular measurement of ryanodine receptor Ca(2+) current.
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DOI：
10.1085/jgp.116.6.845
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发表时间：
2000-12
期刊：
影响因子：
--
通讯作者：
Walsh JV Jr
中科院分区：
文献类型：
--
作者：
ZhuGe R;Fogarty KE;Tuft RA;Lifshitz LM;Sayar K;Walsh JV Jr
Ca2+火花是高度局部化的细胞质Ca2+瞬态，由肌浆网通过ryanodine受体（RyRs）释放Ca2+引起；它们是骨骼肌和心肌中Ca2+全局变化的基本事件。在平滑肌和一些神经元中，Ca2+火花激活火花微域的大电导Ca2+激活的K+通道（BK通道），引起自发瞬态向外电流（STOCs），调节膜电位，从而调节电压门控通道。使用荧光Ca2+指示剂fluo-3和高速宽视场数字成像系统，可以捕获平滑肌细胞火花期间荧光（即信号质量）的总增加，这是第一次在任何系统中使用这种直接方法。信号质量与释放到细胞质中的Ca2+总量成正比，其上升速率与火花（ICa(spark)）期间流过ryr的Ca2+电流成正比。因此，在生理条件下，通过ryr的Ca2+电流可以在细胞内被监测。由于不同火花中ICa（火花）的大小相差超过5倍，Ca2+火花似乎是由多个ryr协调打开引起的。具有相同潜在Ca2+电流的火花引起STOCs，其振幅变化超过三倍，这一发现最好的解释是耦合比的可变性（即火花微域中ryr通道与BK通道的比例）。STOC衰减的时间过程由一个独立于信号质量大小的单一指数近似表示，其时间常数接近BK通道的平均打开时间值，这表明STOC衰减反映了BK通道动力学，而不是膜上[Ca2+]下降的时间过程。计算机模拟确定了由测量范围的ICa（火花）产生的Ca2+浓度的时空分布。在火花开始时，与STOCs的上升速度相比，释放位点200 nm内的Ca2+浓度迅速达到平台或超过BK通道的[Ca2+]EC50。这些发现提示了一个模型，其中BK通道靠近释放位点，暴露于饱和的[Ca2+]中，由BK通道动力学决定stos的上升和下降。RyRs和BK通道之间的信号传导机制可能为Ca2+对细胞微域内各种分子靶点的作用提供了一个模型。
Ca2+ sparks are highly localized cytosolic Ca2+ transients caused by a release of Ca2+ from the sarcoplasmic reticulum via ryanodine receptors (RyRs); they are the elementary events underlying global changes in Ca2+ in skeletal and cardiac muscle. In smooth muscle and some neurons, Ca2+ sparks activate large conductance Ca2+-activated K+ channels (BK channels) in the spark microdomain, causing spontaneous transient outward currents (STOCs) that regulate membrane potential and, hence, voltage-gated channels. Using the fluorescent Ca2+ indicator fluo-3 and a high speed widefield digital imaging system, it was possible to capture the total increase in fluorescence (i.e., the signal mass) during a spark in smooth muscle cells, which is the first time such a direct approach has been used in any system. The signal mass is proportional to the total quantity of Ca2+ released into the cytosol, and its rate of rise is proportional to the Ca2+ current flowing through the RyRs during a spark (ICa(spark)). Thus, Ca2+ currents through RyRs can be monitored inside the cell under physiological conditions. Since the magnitude of ICa(spark) in different sparks varies more than fivefold, Ca2+ sparks appear to be caused by the concerted opening of a number of RyRs. Sparks with the same underlying Ca2+ current cause STOCs, whose amplitudes vary more than threefold, a finding that is best explained by variability in coupling ratio (i.e., the ratio of RyRs to BK channels in the spark microdomain). The time course of STOC decay is approximated by a single exponential that is independent of the magnitude of signal mass and has a time constant close to the value of the mean open time of the BK channels, suggesting that STOC decay reflects BK channel kinetics, rather than the time course of [Ca2+] decline at the membrane. Computer simulations were carried out to determine the spatiotemporal distribution of the Ca2+ concentration resulting from the measured range of ICa(spark). At the onset of a spark, the Ca2+ concentration within 200 nm of the release site reaches a plateau or exceeds the [Ca2+]EC50 for the BK channels rapidly in comparison to the rate of rise of STOCs. These findings suggest a model in which the BK channels lie close to the release site and are exposed to a saturating [Ca2+] with the rise and fall of the STOCs determined by BK channel kinetics. The mechanism of signaling between RyRs and BK channels may provide a model for Ca2+ action on a variety of molecular targets within cellular microdomains.
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影响因子：
56.9
作者：
NELSON, MT;CHENG, H;LEDERER, WJ
通讯作者：
LEDERER, WJ
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作者：
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56.9
作者：
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作者：
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