Fedulova S A, Kostyuk P G, Veselovsky N S
J Physiol. 1985 Feb;359:431-46. doi: 10.1113/jphysiol.1985.sp015594.
Ca2+ inward currents evoked by membrane depolarization have been studied by the intracellular dialysis technique in the somatic membrane of isolated dorsal root ganglion neurones of new-born rats. In about 20% of the investigated cells a hump has been detected on the descending branch of the current-voltage curve, indicating the presence of two populations of Ca2+ channels differing in their potential-dependent characteristics. An initial less regular component of the Ca2+ current was activated at membrane potentials from -75 to -70 mV. Its amplitude reached 0.2-0.9 nA at 14.6 mM-extracellular Ca2+. The activation kinetics of this component could be approximated by the Hodgkin-Huxley equation using the square of the m variable. tau m varied in the range from 8 to 1 ms at potentials between -60 and -25 mV ('fast' Ca2+ current). The second component of the Ca2+ current was activated at membrane depolarizations to between -55 and -50 mV. It could be recorded in all cells investigated and reached a maximum value of 1-7 nA at the same extracellular Ca2+ concentration. This component decreased rapidly during cell dialysis with saline solutions. The decrease could be slowed down by cooling and accelerated by warming the extracellular solution. Intracellular introduction of 3',5'-cAMP together with ATP and Mg2+ not only prevented the decrease but often restored the maximal current amplitude to its initial level. The activation kinetics of this component could also be approximated by a square function, tau m being in the range 16-2.5 ms at membrane potentials between -20 and +3 mV ('slow' Ca2+ current). The fast Ca2+ current inactivated exponentially at sustained depolarizations in a potential-dependent manner, tau h varying from 76 to 35 ms at potentials between -50 and -30 mV. The inactivation of the slow Ca2+ current studied in double-pulse experiments was current-dependent and developed very slowly (time constant of several hundreds of milliseconds). It slowed down even more at low temperature or after substitution of Ba2+ for Ca2+ in the extracellular solution. Both currents could also be carried by Ba2+ and Sr2+, although the ion-selecting properties of the two types of channels showed quantitative differences. Specific blockers of Ca2+ channels (Co2+, Mn2+, Cd2+, Ni2+ or verapamil) exerted similar effects on them. The existence of metabolically dependent and metabolically independent Ca2+ channels in the neuronal membrane and their possible functional role are discussed.
利用细胞内透析技术，在新生大鼠离体背根神经节神经元的胞体膜上，对膜去极化诱发的Ca2+内向电流进行了研究。在约20%的被研究细胞中，电流-电压曲线的下降支上检测到一个峰，这表明存在两类电压依赖性特征不同的Ca2+通道。Ca2+电流的初始不太规则的成分在膜电位从-75 mV到-70 mV时被激活。在细胞外Ca2+浓度为14.6 mM时，其幅度达到0.2 - 0.9 nA。该成分的激活动力学可用霍奇金-赫胥黎方程，采用m变量的平方来近似。在-60 mV至-25 mV的电位下，τm在8至1 ms范围内变化（“快”Ca2+电流）。Ca2+电流的第二个成分在膜去极化至-55 mV至-50 mV之间时被激活。在所有被研究的细胞中都能记录到，在相同的细胞外Ca2+浓度下，其最大值达到1至7 nA。在细胞用盐溶液透析过程中，该成分迅速下降。通过冷却可减缓下降速度，通过加热细胞外溶液可加速下降。细胞内引入3',5'-环磷酸腺苷（cAMP）以及ATP和Mg2+不仅可防止下降，而且常常能使最大电流幅度恢复到初始水平。该成分的激活动力学也可用平方函数近似，在-20 mV至+3 mV的膜电位下，τm在16至2.5 ms范围内（“慢”Ca2+电流）。在持续去极化时，快Ca2+电流以电压依赖性方式呈指数失活，在-50 mV至-30 mV的电位下，τh从76 ms变化到35 ms。在双脉冲实验中研究的慢Ca2+电流的失活是电流依赖性的，且发展非常缓慢（时间常数为几百毫秒）。在低温下或在细胞外溶液中用Ba2+替代Ca2+后，失活进一步减缓。两种电流也都可由Ba2+和Sr2+携带，尽管两类通道的离子选择性特性存在定量差异。Ca2+通道的特异性阻滞剂（Co2+、Mn2+、Cd2+、Ni2+或维拉帕米）对它们产生类似的影响。文中讨论了神经元膜中代谢依赖性和代谢独立性Ca2+通道的存在及其可能的功能作用。
