Kim S J, Chung W H, Rhim H, Eun S-Y, Jung S J, Kim J
Department of Physiology, Kangwon National University College of Medicine, Chunchon 200-701, South Korea.
Neuroscience. 2002;114(4):1139-48. doi: 10.1016/s0306-4522(02)00245-2.
We used tight-seal, whole-cell recording in juvenile rat spinal slices to investigate the action of somatostatin on substantia gelatinosa neurons. Bath application of somatostatin caused a robust and repeatable hyperpolarization or outward current in substantia gelatinosa neurons. Somatostatin inhibited spontaneous action potentials in subpopulation of substantia gelatinosa neurons. The amplitude of dorsal root-evoked excitatory postsynaptic currents and the frequency of spontaneous excitatory postsynaptic currents were not affected by somatostatin. The current induced by somatostatin developed almost instantaneously and did not show any time-dependent inactivation. The current-voltage relationship exhibited inward rectification. The conductance of somatostatin-sensitive current increased with the concentration of external K(+). The reversal potentials in different external K(+) concentrations were close to the K(+) equilibrium potentials. The effect of somatostatin was dose-dependent, with an EC(50) of 113 nM. The somatostatin-sensitive current was blocked by low concentration of extracellular Ba(2+) but not by glibenclamide, an inhibitor of ATP-sensitive K(+) channels. Hyperpolarization-activated cation current in a subpopulation of substantia gelatinosa neurons was not affected by somatostatin. In neurons recorded with an internal solution containing GTPgammaS, somatostatin induced outward current and hyperpolarization that did not reverse on washing. When the spontaneous induction of outward current with GTPgammaS was greatest, somatostatin did not induce any outward currents. Furthermore, intracellular dialysis of GDPbetaS, a G-protein antagonist, abolished the effect of somatostatin. In addition, SST-sensitive neurons were fewer in slices incubated with pertussis toxin than in adjacent control slices incubated without pertussis toxin. These results suggest that somatostatin decreases the postsynaptic membrane excitability of substantia gelatinosa neurons by a pertussis toxin-sensitive G-protein-mediated activation of an inwardly rectifying K(+) conductance.
我们采用紧密封接的全细胞记录方式，在幼年大鼠脊髓切片中研究生长抑素对脊髓胶状质神经元的作用。将生长抑素浴用可使脊髓胶状质神经元产生强烈且可重复的超极化或外向电流。生长抑素抑制了脊髓胶状质神经元亚群中的自发动作电位。背根诱发的兴奋性突触后电流的幅度以及自发兴奋性突触后电流的频率不受生长抑素影响。生长抑素诱导的电流几乎瞬间产生，且未表现出任何时间依赖性失活。电流 - 电压关系呈现内向整流特性。生长抑素敏感电流的电导随细胞外钾离子浓度升高而增加。在不同细胞外钾离子浓度下的反转电位接近钾离子平衡电位。生长抑素的作用呈剂量依赖性，半数有效浓度（EC50）为113 nM。生长抑素敏感电流可被低浓度的细胞外钡离子阻断，但不受格列本脲（一种ATP敏感性钾通道抑制剂）影响。脊髓胶状质神经元亚群中的超极化激活阳离子电流不受生长抑素影响。在用含有鸟苷三磷酸γ - 硫酯（GTPγS）的细胞内液记录的神经元中，生长抑素诱导出外向电流和超极化，冲洗后不反转。当用GTPγS自发诱导外向电流最大时，生长抑素不诱导任何外向电流。此外，G蛋白拮抗剂鸟苷二磷酸β - 硫酯（GDPβS）的细胞内透析消除了生长抑素的作用。另外，与未用百日咳毒素孵育的相邻对照切片相比，用百日咳毒素孵育的切片中对生长抑素敏感的神经元更少。这些结果表明，生长抑素通过百日咳毒素敏感的G蛋白介导的内向整流钾电导激活，降低了脊髓胶状质神经元的突触后膜兴奋性。
