Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
J Neurosci. 2009 Dec 9;29(49):15414-9. doi: 10.1523/JNEUROSCI.4742-09.2009.
Ca(v)1.3 (alpha 1D) L-type Ca(2+) channels have been implicated in substantia nigra (SN) dopamine (DA) neuron pacemaking and vulnerability to Parkinson's disease. These effects may arise from the depolarizing current and cytoplasmic Ca(2+) elevation produced by Ca(v)1.3 channels at subthreshold membrane potentials. However, the assumption that the Ca(2+) selectivity of Ca(v)1.3 channels is essential has not been tested. In this study the properties of SN DA neuron L-type Ca(2+) channels responsible for driving pacemaker activity in juvenile rat brain slices were probed by replacing native channels blocked with the dihydropyridine nimodipine with virtual channels generated by dynamic clamp. Surprisingly, virtual L-type channels that mimic native and recombinant Ca(v)1.3 channels supported pacemaker activity even though dynamic clamp currents are not carried by Ca(2+). This effect is specific because pacemaker activity could not be restored by tonic current injection, virtual nonselective leak channels or virtual NMDA receptors, which share with L-type channels a negative slope conductance region in their current-voltage (I-V) curve. Altering virtual channels showed that the production of pacemaker activity depended on the characteristic voltage dependence of DA neuron L-type channels, while activation kinetics and reversal potential were not critical parameters. Virtual L-type channels also supported slow oscillatory potentials and enhanced firing rate during evoked bursts. Thus, Ca(v)1.3 channel voltage dependence, rather than Ca(2+) selectivity, drives pacemaker activity and amplifies bursts in SN DA neurons.
钙通道 (Ca(v)1.3 [alpha 1D]) L 型钙通道被认为与黑质 (SN) 多巴胺 (DA) 神经元起搏和帕金森病易感性有关。这些效应可能源于 Ca(v)1.3 通道在亚阈值膜电位下产生的去极化电流和细胞质 Ca(2+) 升高。然而，Ca(v)1.3 通道的 Ca(2+) 选择性对于产生这些效应至关重要，这一假设尚未得到验证。在这项研究中，通过用二氢吡啶类尼莫地平阻断内源性通道，用动态钳位产生虚拟通道，来研究负责驱动幼年大鼠脑片 SN DA 神经元起搏活动的 L 型 Ca(2+) 通道的特性。令人惊讶的是，模拟内源性和重组 Ca(v)1.3 通道的虚拟 L 型通道即使在动态钳位电流不携带 Ca(2+)的情况下，也能支持起搏活动。这种效应是特异性的，因为通过强直电流注入、虚拟非选择性漏通道或虚拟 NMDA 受体无法恢复起搏活动，这些通道在其电流-电压 (I-V) 曲线上与 L 型通道共享负斜率电导区。改变虚拟通道表明，起搏活动的产生取决于 DA 神经元 L 型通道的特征电压依赖性，而激活动力学和反转电位不是关键参数。虚拟 L 型通道还支持诱发放电时的缓慢振荡电位和增强的发放率。因此，Ca(v)1.3 通道的电压依赖性而非 Ca(2+) 选择性，驱动 SN DA 神经元的起搏活动并放大爆发。
