Interplay between Na+/Ca2+ exchangers and mitochondria in Ca2+ clearance at the calyx of Held
Interplay between Na+/Ca2+ exchangers and mitochondria in Ca2+ clearance at the calyx of Held
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DOI：
10.1523/jneurosci.0454-05.2005
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发表时间：
2005-06-29
影响因子：
5.3
通讯作者：
Lee, SH
中科院分区：
文献类型：
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作者：
Kim, MH;Korogod, N;Lee, SH
神经末梢Ca2+的清除对于确定重复突触前活动后残余Ca2+的积累至关重要。我们之前发现，依赖K+的Na+/Ca2（+）交换器（NCKXs）在视上大细胞神经元的轴突末端呈现极化分布，并在Ca2+清除中发挥重要作用。然而，NCKXs在突触前终末中的作用尚未被研究。我们通过分析去极化脉冲引起的Ca2+瞬态衰变，研究了NCKX与其他Ca2+清除机制在花萼中的作用。用Li+替代外源Na+抑制Na+/ Ca2+交换可使Ca2+衰减率降低68%。用TEA(+)（四乙基铵）或Li+替代内部K+选择性抑制NCKX可使Ca2+衰减率降低42%，通过减少外部[Na+]对K+独立形式的Na+/ Ca2+交换剂（NCX）的额外抑制可使其额外降低26%。抑制质膜Ca2(+)- atp酶（PMCA）可使Ca2+衰减率降低23%，而抑制SERCA（光滑内质网Ca2+- atp酶）则没有效果。在小的Ca2+瞬态中，线粒体的贡献可以忽略不计，但在[Ca2(+)](i) > 2.5 μ M时，当Na+/ Ca2+交换达到饱和时，线粒体的贡献变得明显。当通过抑制Na+/ Ca2+交换剂或增加Ca2+缓冲剂延长Ca2+瞬态持续时间时，也观察到线粒体的贡献。这些结果表明，在小的Ca2+瞬态（< 2 μ M）下，NCKX（42%）、NCX（26%）和PMCA（23%）清除了Ca2+负载，当Ca2+负载较大或延长时，线粒体参与了Ca2+负载的清除。
The clearance of Ca2+ from nerve terminals is critical for determining the build-up of residual Ca2+ after repetitive presynaptic activity. We found previously that K+- dependent Na+/Ca2(+) exchangers (NCKXs) show polarized distributions in axon terminals of supraoptic magnocellular neurons and play a major role in Ca2+ clearance. The role of NCKXs in presynaptic terminals, however, has not been studied. We investigated the contribution of NCKX in conjunction with other Ca2+ clearance mechanisms at the calyx of Held by analyzing the decay of Ca2+ transients evoked by depolarizing pulses. Inhibition of Na+/ Ca2+ exchange by replacing external Na+ with Li+ decreased the Ca2+ decay rate by 68%. Selective inhibition of NCKX by replacing internal K+ with TEA(+) ( tetraethylammonium) or Li+ decreased the Ca2+ decay rate by 42%, and the additional inhibition of the K+- independent form of Na+/ Ca2+ exchanger (NCX) by reducing external [Na+] caused an additional decrease by 26%. Inhibition of plasma membrane Ca2(+)- ATPase (PMCA) decreased the Ca2+ decay rate by 23%, whereas inhibition of SERCA (smooth endoplasmic reticulum Ca2+- ATPase) had no effect. The contribution of mitochondria was negligible for small Ca2+ transients but became apparent at [Ca2(+)](i) > 2.5 mu M, when Na+/ Ca2+ exchange became saturated. Mitochondrial contribution was also observed when the duration of Ca2+ transients was prolonged by inhibiting Na+/ Ca2+ exchangers or by increasing Ca2+ buffers. These results suggest that, in response to small Ca2+ transients (< 2 mu M), Ca2+ loads are cleared from the calyx of Held by NCKX ( 42%), NCX ( 26%), and PMCA ( 23%), and that mitochondria participate when the Ca2+ load is larger or prolonged.