Regehr W G
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Biophys J. 1997 Nov;73(5):2476-88. doi: 10.1016/S0006-3495(97)78276-6.
Fluorescent indicators were used to detect stimulus-evoked changes in presynaptic levels of intracellular sodium (Na(i)) and calcium (Ca(i)) in granule cell parallel fibers in brain slices from rat cerebellum. Ca(i) increased during stimulation, and three exponentials were needed to approximate its return to prestimulus levels. Ca(i) decayed to approximately 10% of peak levels with tau approximately 100 ms, to approximately 1% of peak values with tau approximately 6 s, and then returned to prestimulus levels with tau approximately 1-2 min. After stimulation, Na(i) accumulated in two phases; one rapid, the other continuing for several hundred milliseconds. The return of Na(i) to prestimulus levels was well approximated by a double exponential decay with time constants of 6-17 s and 2-3 min. Manipulations that prevented calcium entry eliminated both the slow component of sodium entry and the rapid component of Na(i) decay. Reductions of extracellular sodium slowed the rapid phase of Ca(i) decay. These Ca(i) and Na(i) transients were well described by a model in which the plasma membrane of presynaptic boutons contained both a sodium/calcium exchanger and a calcium ATPase (Ca-ATPase). According to this model, immediately after stimulation the sodium/calcium exchanger removes calcium from the terminal more rapidly than does the Ca-ATPase. Eventually, the large concomitant sodium influx brings the exchanger into steady-state, leaving only the Ca-ATPase to remove calcium. This perturbs the equilibrium of the sodium/calcium exchanger, which opposes the Ca-ATPase, leading to a slow return of Ca(i) and Na(i) to resting levels.
荧光指示剂用于检测大鼠小脑脑片颗粒细胞平行纤维中突触前细胞内钠（Na(i)）和钙（Ca(i)）水平的刺激诱发变化。刺激期间Ca(i)增加，需要三个指数函数来近似其恢复到刺激前水平的过程。Ca(i)以约100毫秒的时间常数衰减至峰值水平的约10%，以约6秒的时间常数衰减至峰值的约1%，然后以约1 - 2分钟的时间常数恢复到刺激前水平。刺激后，Na(i)分两个阶段积累；一个快速阶段，另一个持续数百毫秒。Na(i)恢复到刺激前水平可以用时间常数为6 - 17秒和2 - 3分钟的双指数衰减很好地近似。阻止钙进入的操作消除了钠进入的慢成分和Na(i)衰减的快速成分。细胞外钠的减少减缓了Ca(i)衰减的快速阶段。这些Ca(i)和Na(i)瞬变可以用一个模型很好地描述，在该模型中，突触前终扣的质膜包含钠/钙交换器和钙ATP酶（Ca - ATPase）。根据这个模型，刺激后立即，钠/钙交换器比Ca - ATPase更快地从终末去除钙。最终，大量伴随的钠内流使交换器进入稳态，只剩下Ca - ATPase去除钙。这扰乱了与Ca - ATPase相反的钠/钙交换器的平衡，导致Ca(i)和Na(i)缓慢恢复到静息水平。
