Substance P: ionic basis for depolarizing responses of mouse spinal cord neurons in cell culture
Substance P: ionic basis for depolarizing responses of mouse spinal cord neurons in cell culture
复制标题
P物质：细胞培养物中小鼠脊髓神经元去极化反应的离子基础
作者：
L. Nowak;R. Macdonald
用细胞内记录方法研究了P物质（SP）对原代分离培养的小鼠脊髓神经元突触后作用的离子基础。SP和一种类似物，eledoisin相关肽（ERP），施加到单个神经元的压力喷射的肽含有解决方案，从钝（2至10微米）玻璃微量移液管。SP和ERP具有相似的兴奋作用，通过降低膜电导增加自发活动和去极化神经元。去极化反应不逆转细胞内注射氯离子，这表明SP反应没有导致氯离子电导下降。SP和ERP反应没有被细胞外四乙基铵离子（TEA+），但减少或消除细胞内TEA+，表明SP减少钾电导（gK）。最后，SP和ERP反应较大时，神经元去极化和较小时，细胞超极化，和外推的逆转电位的肽反应比静息膜电位负10至30 mV。因此，可以得出结论，SP通过降低膜钾电导来使脊髓神经元去极化。然而，SP和ERP反应极性没有明显逆转，即使在膜电位比预期的钾平衡电位更负。此外，SP反应的外推逆转电位（RPeS）与细胞外钾浓度（[K+]o）的对数呈线性关系，如对[K+]o浓度为10，15，20，和40 mM，但去极化程度高于[K+]的预测由于通过胆碱替代减少细胞外钠并不改变对钾的能斯特方程的偏离，结论：SP降低了电压依赖性钾电导，这种电导在非常负的电位下不存在，在静息膜电位下存在，并由膜去极化激活。因此，SP降低电导，其看起来类似于交感神经节神经元中的毒蕈碱敏感性钾电导（Brown，D.一、和公共关系。亚当斯（1980）自然283：673-676）。
Intracellular recording methods were used to investigate the ionic basis for the postsynaptic actions of substance P (SP) on mouse spinal cord neurons grown in primary dissociated cell culture. SP and an analog, eledoisin-related peptide (ERP), were applied to single neurons by pressure ejection of peptide-containing solutions from blunt (2- to 10-micrometers) glass micropipettes. SP and ERP had similar excitatory actions, increasing spontaneous activity and depolarizing neurons by decreasing membrane conductance. Depolarizing responses were not inverted by intracellular injection of chloride ions, suggesting that SP responses did not result from decreased chloride conductance. SP and ERP responses were not abolished by extracellular tetraethylammonium ions (TEA+) but were reduced or eliminated by intracellular TEA+, suggesting that SP reduced a potassium conductance (gK). Finally, SP and ERP responses were larger when neurons were depolarized and smaller when the cells were hyperpolarized, and extrapolated reversal potentials for the peptide responses were 10 to 30 mV more negative than resting membrane potential. Thus, it was concluded that SP depolarized spinal cord neurons by decreasing a membrane potassium conductance. However, SP and ERP response polarity was not clearly reversed even at membrane potentials more negative than the expected potassium equilibrium potential. Moreover, extrapolated reversal potentials (RPeS) of SP responses varied linearly with the logarithm of extracellular potassium concentration ([K+]o) as predicted by the Nernst equation for potassium in [K+]o concentrations of 10, 15, 20, and 40 mM but were more depolarized than predicted for [K+]o concentrations of 1 and 5 mM. Since reduction of extracellular sodium by choline substitution did not alter the deviation from the Nernst equation for potassium, it was concluded that SP decreased a voltage- dependent potassium conductance which was absent at very negative potentials, present at resting membrane potential, and activated by membrane depolarization. Thus, SP decreases a conductance which appears similar to the muscarine-sensitive potassium conductance in sympathetic ganglion neurons (Brown, D. A., and P. R. Adams (1980) Nature 283: 673–676).