Becchetti A, Arcangeli A, Del Bene M R, Olivotto M, Wanke E
Department of General Physiology and Biochemistry, University of Milan, Italy.
Biophys J. 1992 Oct;63(4):954-65. doi: 10.1016/S0006-3495(92)81665-X.
The properties of low (LVA) and high (HVA) voltage-activated calcium currents were investigated in rat sensory neurons and a murine neuroblastoma cell line exposed to various concentrations of intra- or extracellular monovalent ([c+]i/o) and trivalent ([c3+]i/o) cations. In neurons, when [c+]i was changed from 150 to 20 mM, positive shifts of 18-28 mV were observed in activation curves of both LVA and HVA currents, as well as in LVA inactivation curves. Extracellularly, in divalent-free solutions, [c+]o of 20-50 mM produced medium (12-22 mV) negative shifts of the LVA channel properties. These data were used to estimate, by a "screening" model, a negative surface charge density around neuron's calcium channels of 1/1,000 and 1/1,325 eA-2 at the outside or inside face, respectively. In the presence of physiological concentrations of divalent cations, [c+]o of 20-60 mM caused smaller (4-11 mV) negative shifts of the activation and inactivation curves, which can be explained by assuming a partial neutralization of negative charges by divalent cations. By applying the above procedure to LVA channels of neuroblastoma cells, the ratio of extra- to intracellular surface charge density turned out to be more than tenfold higher than in neurons. Effects produced by [c3+]i/o were not in agreement with expectations based on screening or binding models.
在大鼠感觉神经元和暴露于不同浓度细胞内或细胞外单价（[c+]i/o）和三价（[c3+]i/o）阳离子的小鼠神经母细胞瘤细胞系中，研究了低电压激活（LVA）和高电压激活（HVA）钙电流的特性。在神经元中，当[c+]i从150 mM变为20 mM时，LVA和HVA电流的激活曲线以及LVA失活曲线均出现18 - 28 mV的正向偏移。在细胞外，在无二价阳离子的溶液中，20 - 50 mM的[c+]o使LVA通道特性产生中等程度（12 - 22 mV）的负向偏移。利用这些数据，通过“筛选”模型估计，神经元钙通道外表面和内表面的负表面电荷密度分别为1/1,000和1/1,325 eA-2。在存在生理浓度二价阳离子的情况下，20 - 60 mM的[c+]o使激活曲线和失活曲线产生较小（4 - 11 mV）的负向偏移，这可以通过假设二价阳离子部分中和负电荷来解释。将上述方法应用于神经母细胞瘤细胞的LVA通道时，细胞外与细胞内表面电荷密度之比比神经元中的高出十多倍。[c3+]i/o产生的效应与基于筛选或结合模型的预期不一致。
