Calupca M A, Prior C, Merriam L A, Hendricks G M, Parsons R L
Department of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington, VT 05405, USA.
J Physiol. 2001 Apr 1;532(Pt 1):217-27. doi: 10.1111/j.1469-7793.2001.0217g.x.
Presynaptic function was investigated at K+-stimulated motor nerve terminals in snake costocutaneous nerve muscle preparations exposed to carbonyl cyanide m-chlorophenylhydrazone (CCCP, 2 M), oligomycin (8 g x ml(-1)) or CCCP and oligomycin together. Miniature endplate currents (MEPCs) were recorded at -150 mV with two-electrode voltage clamp. With all three drug treatments, during stimulation by elevated K+ (35 mM), MEPC frequencies initially increased to values > 350 s(-1), but then declined. The decline occurred more rapidly in preparations treated with CCCP or CCCP and oligomycin together than in those treated with oligomycin alone. Staining with FM1-43 indicated that synaptic vesicle membrane endocytosis occurred at some CCCP- or oligomycin-treated nerve terminals after 120 or 180 min of K+ stimulation, respectively. The addition of glucose to stimulate production of ATP by glycolysis during sustained K+ stimulation attenuated the decline in MEPC frequency and increased the percentage of terminals stained by FM1-43 in preparations exposed to either CCCP or oligomycin. We propose that the decline in K+-stimulated quantal release in preparations treated with CCCP, oligomycin or CCCP and oligomycin together could result from a progressive elevation of intracellular calcium concentration ([Ca2+]i). For oligomycin-treated nerve terminals, a progressive elevation of [Ca2+]i could occur as the cytoplasmic ATP/ADP ratio decreases, causing energy-dependent Ca2+ buffering mechanisms to fail. The decline in MEPC frequency could occur more rapidly in preparations treated with CCCP or CCCP and oligomycin together because mitochondrial Ca2+ buffering and ATP production were both inhibited. Therefore, the proposed sustained elevation of [Ca2+]i could occur more rapidly.
在暴露于羰基氰化物间氯苯腙（CCCP，2 μM）、寡霉素（8 μg/ml）或CCCP与寡霉素联合作用的蛇肋皮神经肌肉标本中，研究了钾离子刺激下运动神经末梢的突触前功能。采用双电极电压钳在 -150 mV 记录微小终板电流（MEPCs）。在所有三种药物处理中，在高钾（35 mM）刺激期间，MEPC 频率最初增加至 > 350 s⁻¹，但随后下降。与单独用寡霉素处理的标本相比，用CCCP或CCCP与寡霉素联合处理的标本中下降更快。用FM1-43染色表明，在钾离子刺激120或180分钟后，分别在一些经CCCP或寡霉素处理的神经末梢发生了突触囊泡膜内吞作用。在持续钾离子刺激期间添加葡萄糖以通过糖酵解刺激ATP生成，减弱了MEPC频率的下降，并增加了暴露于CCCP或寡霉素的标本中被FM1-43染色的神经末梢百分比。我们提出，用CCCP、寡霉素或CCCP与寡霉素联合处理的标本中，钾离子刺激下量子释放的下降可能是由于细胞内钙浓度（[Ca²⁺]i）的逐渐升高所致。对于经寡霉素处理的神经末梢，随着细胞质ATP/ADP比值降低，[Ca²⁺]i可能会逐渐升高，导致能量依赖的Ca²⁺缓冲机制失效。在用CCCP或CCCP与寡霉素联合处理的标本中，MEPC频率的下降可能更快，因为线粒体Ca²⁺缓冲和ATP生成均受到抑制。因此，所提出的[Ca²⁺]i持续升高可能会更快发生。
