Spike frequency decoding and autonomous activation of Ca2+-calmodulin-dependent protein kinase II in dorsal root ganglion neurons
Spike frequency decoding and autonomous activation of Ca2+-calmodulin-dependent protein kinase II in dorsal root ganglion neurons
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DOI：
10.1523/jneurosci.21-17-06694.2001
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发表时间：
2001-09-01
影响因子：
5.3
通讯作者：
Fields, RD
中科院分区：
文献类型：
--
作者：
Eshete, F;Fields, RD
钙-钙调蛋白激酶（CaMKII）的自主激活被认为是解码由动作电位放电引起的Ca2+峰值频率的分子机制，但尚未在完整的神经元中进行研究。这在培养的小鼠DRG神经元中进行了研究，使用共聚焦测量[Ca2+](i)和CaMKII自磷酸化和自主活性的生化测量。使用不同频率的电刺激，我们发现CaMKII自主活动在类似的45次脉冲后达到接近最高水平，无论发射频率如何（1-10 Hz），并且自主活动随着刺激时间的延长而下降。CaMKII的频率依赖性激活仅限于0.1-1 Hz范围内的尖峰频率，尽管在较高频率（1-30 Hz）下[Ca2+](i)显着增加。刺激前测量到的高水平自主活动和动作电位诱导的相对较长的Ca2+峰值持续时间（类似于300 msec）与CaMKII解码动作电位的较低频率范围一致。基础条件下的高自主活性与细胞外[Ca2+]有关，独立于[Ca2+]的变化(i)，与突触或自发冲动活动无关。CaMKII响应动作电位短暂爆发的自主活性与Ca2+瞬态频率的相关性强于与[Ca2+]浓度的相关性(i)。综上所述，CaMKII可以解码这些神经元中0.1至1hz之间的调频响应，但可能需要其他机制来解码更高的频率。另外，CaMKII可能介导亚细胞微域的高频反应，其中酶维持在低水平的自主活性或Ca2+瞬态具有更快的动力学。
Autonomous activation of calcium-calmodulin kinase (CaMKII) has been proposed as a molecular mechanism for decoding Ca2+ spike frequencies resulting from action potential firing, but this has not been investigated in intact neurons. This was studied in mouse DRG neurons in culture using confocal measurements of [Ca2+](i) and biochemical measurements of CaMKII autophosphorylation and autonomous activity. Using electrical stimulation at different frequencies, we find that CaMKII autonomous activity reached near maximal levels after similar to 45 impulses, regardless of firing frequency (1-10 Hz), and autonomous activity declined with prolonged stimulation. Frequency-dependent activation of CaMKII was limited to spike frequencies in the range of 0.1-1 Hz, despite marked increases in [Ca2+](i) at higher frequencies (1-30 Hz). The high levels of autonomous activity measured before stimulation and the relatively long duration of Ca2+ spikes induced by action potentials (similar to 300 msec) are consistent with the lower frequency range of action potential decoding by CaMKII. The high autonomous activity under basal conditions was associated with extracellular [Ca2+], independently from changes in [Ca2+](i), and unrelated to synaptic or spontaneous impulse activity. CaMKII autonomous activity in response to brief bursts of action potentials correlated better with the frequency of Ca2+ transients than with the concentration of [Ca2+](i). In conclusion, CaMKII may decode frequency-modulated responses between 0.1 and 1 Hz in these neurons, but other mechanisms may be required to decode higher frequencies. Alternatively, CaMKII may mediate high-frequency responses in subcellular microdomains in which the enzyme is maintained at a low level of autonomous activity or the Ca2+ transients have faster kinetics.