Hirokawa N, Heuser J E
J Cell Biol. 1981 Jan;88(1):160-71. doi: 10.1083/jcb.88.1.160.
Taking advantage of the fact that nerve terminal mitochondria swell and sequester calcium during repetitive nerve stimulation, we here confirm that this change is caused by calcium influx into the nerve and use this fact to show that botulinum toxin abolishes such calcium influx. The optimal paradigm for producing the mitochondrial changes in normal nerves worked out to be 5 min of stimulation at 25 Hz in frog Ringer's solution containing five time more calcium than normal. Applying this same stimulation paradigm to botulinum-intoxicated nerves produced no mitochondrial changes at all. Only when intoxicated nerves were stimulated in 4-aminopyridine (which grossly exaggerates calcium currents in normal nerves) or when they were soaked in black widow spider venom (which is a nerve-specific calcium ionophore) could nerve mitochondria be induced to swell and accumulate calcium. These results indicate that nerve mitochondria are not damaged directly by the toxin and point instead to a primary inhibition of the normal depolarization-evoked calcium currents that accompany nerve activity. Because these currents normally provide the calcium that triggers transmitter secretion from the nerve, this demonstration of their inhibition helps to explain how botulinum toxin paralyzes.
利用神经末梢线粒体在重复性神经刺激过程中肿胀并隔离钙这一事实，我们在此证实这种变化是由钙流入神经所引起的，并利用这一事实表明肉毒杆菌毒素可消除这种钙流入。在含有的钙比正常情况多五倍的青蛙林格氏液中，以25赫兹刺激5分钟被证明是在正常神经中产生线粒体变化的最佳模式。将同样的刺激模式应用于肉毒杆菌中毒的神经，根本不会产生线粒体变化。只有当中毒神经在4-氨基吡啶中受到刺激（这会极大地夸大正常神经中的钙电流），或者当它们浸泡在黑寡妇蜘蛛毒液中（这是一种神经特异性钙离子载体）时，神经线粒体才会被诱导肿胀并积累钙。这些结果表明神经线粒体并非直接被毒素损害，而是表明正常的伴随神经活动的去极化诱发钙电流受到了原发性抑制。由于这些电流通常提供触发神经递质分泌的钙，对其抑制的这一证明有助于解释肉毒杆菌毒素是如何导致麻痹的。
