Robitaille R, Garcia M L, Kaczorowski G J, Charlton M P
Department of Physiology, University of Toronto, Ontario, Canada.
Neuron. 1993 Oct;11(4):645-55. doi: 10.1016/0896-6273(93)90076-4.
We examined, using physiological and morphological techniques, the distribution of Ca(2+)-gated K+ (gKca) channels relative to the location of Ca2+ channels and transmitter release sites at the frog neuromuscular junction (NM). Charybdotoxin (ChTx) and iberiotoxin, blockers of gKca channels with large conductances, increase transmitter release at the frog NMJ. Intracellular Ca2+ buffers with rapid binding kinetics, dimethyl BAPTA and BAPTA, prevented the effect of ChTx, but EGTA, a Ca2+ buffer with similar affinity for Ca2+ but slower binding kinetics, did not. Dimethyl BAPTA and BAPTA, but not EGTA, caused a temporary increase in transmitter release. Labeling of gKca channels with ChTx-biotin revealed a series of bands located at the sites of Ca2+ channels, but this labeling did not occur in denervated preparations. Cross sections of NMJs revealed that gKca channels are clustered in the presynaptic membrane facing the postsynaptic membrane. We conclude that gKca channels are strategically clustered at the neurotransmitter release sites, where they can be quickly activated by Ca2+ entering the terminal.
我们运用生理学和形态学技术，研究了蛙神经肌肉接头（NM）处钙门控钾通道（gKca）相对于钙通道位置和递质释放位点的分布情况。大电导gKca通道的阻滞剂查利毒素（ChTx）和埃博毒素可增加蛙神经肌肉接头处的递质释放。具有快速结合动力学的细胞内钙缓冲剂二甲基BAPTA和BAPTA可阻止ChTx的作用，但对钙具有相似亲和力但结合动力学较慢的钙缓冲剂EGTA则不能。二甲基BAPTA和BAPTA而非EGTA会导致递质释放暂时增加。用ChTx-生物素标记gKca通道显示出一系列位于钙通道位点的条带，但这种标记在去神经支配的标本中未出现。神经肌肉接头的横截面显示，gKca通道聚集在面向突触后膜的突触前膜中。我们得出结论，gKca通道在神经递质释放位点进行策略性聚集，在那里它们可以被进入终末的钙快速激活。
