McNaughton N C, Randall A D
Division of Neurobiology, MRC Laboratory of Molecular Biology, Cambridge, U.K.
Neuropharmacology. 1997 Jul;36(7):895-915. doi: 10.1016/s0028-3908(97)00085-3.
We have characterized the properties of the human N-type Ca2+ channel produced by the stable co-expression of the alpha(1B-1), alpha(2b)delta and beta(1b) subunits. The channel displayed the expected pharmacology with respect to the toxins omega-CTx-GVIA and omega-CTx-MVIIC, which depressed currents in a voltage-independent fashion. We characterized a variety of biophysical properties of the channel under conditions in which either Ca2+, Ba2+ or Sr2+ was the sole extracellular divalent ion. In all three ions, current-voltage relationships revealed that the channel was clearly high-voltage activated. Current activation was significantly slower in Ca2+ than either Sr2+ or Ba2+. Construction of conductance-voltage relationships from tail current measurements indicated that the channel was more high-voltage activated in Ca2+ than in either Sr2+ or Ba2+. The rank order of current amplitude at +4 mV was Ba2+ > Sr2+ > or = Ca2+. Elevation of the extracellular concentration of Ba2+ increased maximal current amplitude and shifted the current-voltage relationship to the right. In all three ions channel inactivation was complex consisting of three distinct exponentials. Recovery from inactivation was slow taking several seconds to reach completion. Steady-state inactivation curves revealed that channel inactivation became detectable at holding potentials of between -101 and -91 mV depending on the permeating species. The rank order of mid-points of steady state inactivation was (most negative) Sr2+ > Ca2+ > Ba2+ (most positive). Deactivation of the N-type Ca2+ channel was voltage-dependent and very fast in all three ions. The deactivation rate in Ba2+ was significantly slower than that in both Ca2+ and Sr2+, however the voltage-dependence of deactivation rate was indistinguishable in all three ions.
我们已经对通过稳定共表达α(1B - 1)、α2δ和β1b亚基产生的人N型Ca2+通道的特性进行了表征。该通道在毒素ω-CTx - GVIA和ω-CTx - MVIIC方面表现出预期的药理学特性，这些毒素以电压非依赖性方式抑制电流。我们在Ca2+、Ba2+或Sr2+为唯一细胞外二价离子的条件下，对该通道的多种生物物理特性进行了表征。在所有这三种离子中，电流-电压关系表明该通道明显是高电压激活的。Ca2+中的电流激活明显比Sr2+或Ba2+中的慢。通过尾电流测量构建的电导-电压关系表明，该通道在Ca2+中比在Sr2+或Ba2+中更易被高电压激活。在+4 mV时电流幅度的顺序为Ba2+ > Sr2+ >或 = Ca2+。细胞外Ba2+浓度的升高增加了最大电流幅度，并使电流-电压关系向右移动。在所有这三种离子中，通道失活都很复杂，由三个不同的指数组成。从失活中恢复很慢，需要几秒钟才能完成。稳态失活曲线表明，根据通透离子的种类，在 - 101至 - 91 mV之间的保持电位下可检测到通道失活。稳态失活中点的顺序为（最负）Sr2+ > Ca2+ > Ba2+（最正）。N型Ca2+通道的去激活是电压依赖性的，并且在所有这三种离子中都非常快。然而，Ba2+中的去激活速率明显比Ca2+和Sr2+中的慢，不过在所有这三种离子中去激活速率的电压依赖性是无法区分的。
