Whim M D, Kaczmarek L K
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066, USA.
J Neurosci. 1998 Nov 15;18(22):9171-80. doi: 10.1523/JNEUROSCI.18-22-09171.1998.
The bag cell neurons of Aplysia are a cluster of cells that control egg laying behavior. After brief synaptic stimulation, they depolarize and fire spontaneously for up to 30 min. During the first few seconds of this afterdischarge, the action potentials of the bag cell neurons undergo pronounced broadening. Single bag cell neurons in culture also show spike broadening in response to repeated depolarizations. This broadening is frequency-dependent and associated with the induction of a depolarizing afterpotential lasting minutes. In some neurons the depolarizing afterpotential is sufficient to trigger spontaneous firing. To test the possibility that spike broadening during stimulation is required to trigger the depolarizing afterpotential, we eliminated frequency-dependent broadening by heterologous expression of the Kv3.1 potassium channel. This channel has rapid activation and deactivation kinetics and no use-dependent inactivation. Expression of Kv3.1 prevented spike broadening and also eliminated the depolarizing afterpotential. Measurements of the integral of calcium current during voltage commands, which simulated the action potentials of the control neurons and those expressing Kv3.1, indicate that spike broadening produces up to a fivefold increase in calcium entry. Manipulations that limit calcium entry during action potentials or chelation of intracellular calcium using BAPTA AM prevented the induction of the depolarizing afterpotential. We conclude that spike broadening is essential for the induction of the depolarizing afterpotential probably by regulating calcium influx and suggest that one of the physiological roles of spike broadening may be to regulate long-term changes in neuronal excitability.
海兔的袋状细胞神经元是一组控制产卵行为的细胞。经过短暂的突触刺激后，它们会去极化并自发放电长达30分钟。在这种后放电的最初几秒钟内，袋状细胞神经元的动作电位会明显变宽。培养中的单个袋状细胞神经元在反复去极化时也会出现峰电位变宽。这种变宽是频率依赖性的，并且与持续数分钟的去极化后电位的诱导有关。在一些神经元中，去极化后电位足以触发自发放电。为了测试刺激期间峰电位变宽是否是触发去极化后电位所必需的，我们通过异源表达Kv3.1钾通道消除了频率依赖性变宽。该通道具有快速的激活和失活动力学，且无使用依赖性失活。Kv3.1的表达阻止了峰电位变宽，也消除了去极化后电位。在电压指令期间对钙电流积分的测量，模拟了对照神经元和表达Kv3.1的神经元的动作电位，结果表明峰电位变宽使钙内流增加了五倍。在动作电位期间限制钙内流或使用BAPTA AM螯合细胞内钙的操作可阻止去极化后电位的诱导。我们得出结论，峰电位变宽可能通过调节钙内流对于去极化后电位的诱导至关重要，并表明峰电位变宽的生理作用之一可能是调节神经元兴奋性的长期变化。
