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

越来越多的疾病被描述为电压门控离子通道内的突变是潜在的分子缺陷。纯合子的失动小鼠，即totering （tg）和leaner （tg^<la>）小鼠，在P/ q型Ca^<2+>通道α_< la>亚基基因中存在突变。除了这两种共济失调小鼠外，第三种隐性神经突变小鼠滚动名古屋（tg^<rol>）表现出运动协调性和僵硬性差。共济失调症状的严重程度排序为tg^<la> > tg^<rol> > tg。为了探讨症状严重程度与通道特性之间的关系，我们在此描述了与正常、tg、tg^<la>和tg^<rol>小鼠分离的小脑浦肯野细胞Ca^<2+>通道的电生理特性。tg^<rol>（247±14,n = 32）、tg（184±18,n = 27）和tg^<la>（123±9,n = 25）小鼠的电流密度（333±18 pA/pF, n = 67，正常小鼠）显著降低。尾电流的峰值振幅反射通道激活,安装了一个玻耳兹曼函数,电压half-maximal激活和边坡因素分别为-28.0±1.1 mV和4.9±0.5 mV (n = 11)对正常小鼠,-28.3±1.1,4.7±0.3 (n = 13) tg老鼠,-20.3±1.7,5.8±0.2 (n = 13) tg ^ <方式>老鼠和-19.2±1.3,5.4±0.3 (n = 13) tg ^ <洛杉矶>小鼠,分别。tg^<rol>和tg^<la>的激活曲线向去极化方向移动，导致Ca^<2+>通道活性降低，尽管在tg小鼠中保持正常。结果表明，电流减少和门控行为的偏差协同降低了小脑浦肯野细胞p型Ca^<2+>通道活性，可能与共济失调小鼠的神经病理有关。

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.