Electrophysiological study of mutant P-type Ca^<2+> channels causing diseases

越来越多的疾病被描述，其中电压门控离子通道内的突变是潜在的分子缺陷。纯合子共济失调小鼠，摇摇欲坠(Tg)和较瘦(Tg^&lt；la&gt；)小鼠，在P/Q型钙通道α_&lt；la&gt；亚单位基因上有突变。除了这两只共济失调小鼠，第三个隐性神经突变小鼠，滚动名古屋(Tg^&lt；rol&gt；)，表现出较差的运动协调性和僵硬。共济失调症状的严重程度排序为Tg；lt；la；gt；tg；为了探讨症状严重程度与通道特性之间的关系，我们在此研究了正常、TG、TG；lt；1a&gt；和Tg^&lt；rol&gt；小鼠小脑浦肯野细胞钙通道的电生理特性。Tg^&lt；rol&gt；(247±14，n=32)、Tg(184±18，n=27)和Tg^&lt；1a&gt；(123±9，n=25)小鼠的电流密度显著降低(333±18pA/pF，n=67)。用单一Boltzmann函数拟合反映通道激活的尾电流峰值，其中正常小鼠的半最大激活电压和斜率因子分别为-28.0±1.1 mV和4.9±0.5 mV(n=11)，转基因小鼠分别为-28.3±1.1 mV和4.7±0.3(n=13)，Tg^&lt；rol&gt；Tg^&lt；la&gt；小鼠分别为-19.2±1.3和5.4±0.3(n=13)。Tg^&lt；rol&gt；和Tg^&lt；la&gt；的激活曲线向去极化方向移动，导致Ca^&lt；2&gt；通道活性降低，但在Tg小鼠中仍保持正常。结果提示，电流的减少和门控行为的偏离协同降低了小脑浦肯野细胞的P型钙通道活性，可能参与了共济失调小鼠的神经病理过程。

An increasing number of disorders have been described in which mutations within voltage-gated ion channels are the underlying molecular defect. Homozygous ataxic mice, tottering (tg) and leaner (tg^<la>) mice, have mutations in the P/Q-type Ca^<2+> channelα_<lA>, subunit gene. Besides these two ataxic mice the third recessive neurological mouse mutant, rolling Nagoya (tg^<rol>), manifests poor motor coordination and stiffness. The rank order of severity of the ataxic symptoms is tg^<la> > tg^<rol> > tg. To explore the relationship between severity of symptoms and channel properties, we have here characterized the electrophysiological properties of Ca^<2+> channels in cerebellar Purkinje cells dissociated from the normal, tg, tg^<la> and tg^<rol> mice. Current density (333 ± 18 pA/pF, n = 67, for normal mice) was significantly reduced in tg^<rol> (247 ± 14, n = 32), tg (184 ± 18, n = 27) and tg^<la> (123 ± 9, n = 25) mice. Peak amplitudes of tail currents, which reflect channel activation, were fitted by a single Boltzmann function, where the voltages for half-maximal activation and slope factors were -28.0 ± 1.1 mV and 4.9 ± 0.5 mV (n = 11) for normal mice, -28.3 ± 1.1 and 4.7 ± 0.3 (n = 13) for tg mice, -20.3 ± 1.7 and 5.8 ± 0.2 (n = 13) for tg^<rol> mice and -19.2 ± 1.3 and 5.4 ± 0.3 (n = 13) for tg^<la> mice, respectively. Activation curves for tg^<rol> and tg^<la> were shifted in the depolarizing direction resulting in reduction of Ca^<2+> channel activity, although it remained normal in tg mice. The results suggest that current reduction and deviation of gating behavior synergically diminish P-type Ca^<2+> channel activity in cerebellar Purkinje cells and may contribute to the neuropathology of the ataxic mice.