Baccei M L, Kocsis J D
Department of Neurology, Yale University School of Medicine, New Haven 06510, USA.
J Neurophysiol. 2000 Apr;83(4):2227-38. doi: 10.1152/jn.2000.83.4.2227.
The effect of sciatic nerve injury on the somatic expression of voltage-gated calcium currents in adult rat cutaneous afferent dorsal root ganglion (DRG) neurons identified via retrograde Fluoro-gold labeling was studied using whole cell patch-clamp techniques. Two weeks after a unilateral ligation and transection of the sciatic nerve, the L(4)-L(5) DRG were dissociated and barium currents were recorded from cells 3-10 h later. Cutaneous afferents (35-50 microm diam) were classified as type 1 (possessing only high-voltage-activated currents; HVA) or type 2 (having both high- and low-voltage-activated currents). Axotomy did not change the percentage of neurons exhibiting a type 2 phenotype or the properties of low-threshold T-type current found in type 2 neurons. However, in type 1 neurons the peak density of HVA current available at a holding potential of -60 mV was reduced in axotomized neurons (83.9 +/- 5.6 pA/pF, n = 53) as compared with control cells (108.7 +/- 6.9 pA/pF, n = 58, P < 0.01, unpaired t-test). A similar reduction was observed at more negative holding potentials, suggesting differences in steady-state inactivation are not responsible for the effect. Separation of the type 1 cells into different size classes indicates that the reduction in voltage-gated barium current occurs selectively in the larger (capacitance >80 pF) cutaneous afferents (control: 112.4 +/- 10.6 pA/pF, n = 30; ligated: 72.6 +/- 5.0 pA/pF, n = 36; P < 0.001); no change was observed in cells with capacitances of 45-80 pF. Isolation of the N- and P¿Q-type components of the HVA current in the large neurons using omega-conotoxin GVIA and omega-agatoxin TK suggests a selective reduction in N-type barium current after nerve injury, as the density of omega-CgTx GVIA-sensitive current decreased from 56.9 +/- 6.6 pA/pF in control cells (n = 13) to 31.3 +/- 4.6 pA/pF in the ligated group (n = 12; P < 0.005). The HVA barium current of large cutaneous afferents also demonstrates a depolarizing shift in the voltage dependence of inactivation after axotomy. Injured type 1 cells exhibited faster inactivation kinetics than control neurons, although the rate of recovery from inactivation was similar in the two groups. The present results indicate that nerve injury leads to a reorganization of the HVA calcium current properties in a subset of cutaneous afferent neurons.
采用全细胞膜片钳技术，研究了坐骨神经损伤对经逆行荧光金标记鉴定的成年大鼠皮肤传入背根神经节（DRG）神经元电压门控钙电流的体细胞表达的影响。在单侧结扎并切断坐骨神经两周后，分离L(4)-L(5) DRG，并在3 - 10小时后记录细胞的钡电流。皮肤传入神经元（直径35 - 50微米）分为1型（仅具有高压激活电流；HVA）或2型（同时具有高压和低压激活电流）。轴突切断术并未改变表现出2型表型的神经元百分比或2型神经元中低阈值T型电流的特性。然而，在1型神经元中，与对照细胞（108.7±6.9 pA/pF，n = 58，P < 0.01，非配对t检验）相比，轴突切断的神经元在-60 mV的钳制电位下可用的HVA电流峰值密度降低（83.9±5.6 pA/pF，n = 53）。在更负的钳制电位下也观察到类似的降低，表明稳态失活的差异不是造成这种效应的原因。将1型细胞分为不同大小类别表明，电压门控钡电流的降低选择性地发生在较大（电容>80 pF）的皮肤传入神经元中（对照：112.4±10.6 pA/pF，n = 30；结扎：72.6±5.0 pA/pF；n = 36；P < 0.001）；电容为45 - 80 pF的细胞未观察到变化。使用ω-芋螺毒素GVIA和ω-阿加毒素TK分离大神经元中HVA电流的N型和P/Q型成分表明，神经损伤后N型钡电流选择性降低，因为ω-CgTx GVIA敏感电流密度从对照细胞中的56.9±陆.6 pA/pF（n = 13）降至结扎组中的31.3±4.6 pA/pF（n = 12；P < 0.005）。大皮肤传入神经元的HVA钡电流在轴突切断后失活的电压依赖性也表现出去极化偏移。尽管两组从失活中恢复的速率相似，但损伤的1型细胞比对照神经元表现出更快的失活动力学。目前的结果表明，神经损伤导致皮肤传入神经元亚群中HVA钙电流特性的重组。
