Chaban V V, Mayer E A, Ennes H S, Micevych P E
Laboratory of Neuroendocrinology, Brain Research Institute, Department of Neurobiology, Mental Retardation Research Center, David Geffen School of Medicine, University of California, Los Angeles, 73-074 CHS, Charles E. Young Drive South, 90095-1786, USA.
Neuroscience. 2003;118(4):941-8. doi: 10.1016/s0306-4522(02)00915-6.
Estrogen has been implicated in modulation of pain processing. Although this modulation occurs within the CNS, estrogen may also act on primary afferent neurons whose cell bodies are located within the dorsal root ganglia (DRG). Primary cultures of rat DRG neurons were loaded with Fura-2 and tested for ATP-induced changes in intracellular calcium concentration (Ca(2+)) by fluorescent ratio imaging. ATP, an algesic agent, induces Ca(2+) changes via activation of purinergic 2X (P2X) type receptors and voltage-gated Ca(2+) channels (VGCC). ATP (10 microM) caused increased Ca(2+) transients (226.6+/-16.7 nM, n = 42) in 53% of small to medium DRG neurons. A 5-min incubation with 17 beta-estradiol (100 nM) inhibited ATP-induced Ca(2+) (164+/-14.6 nM, P<0.05) in 85% of the ATP-responsive DRG neurons, whereas the inactive isomer 17 alpha-estradiol had no effect. Both the mixed agonist/antagonist tamoxifen (1 microM) and specific estrogen receptor antagonist ICI 182780 (1 microM) blocked the estradiol inhibition of ATP-induced Ca(2+) transients. Estradiol coupled to bovine serum albumin, which does not diffuse through the plasma membrane, blocked ATP-induced Ca(2+), suggesting that estradiol acts at a membrane-associated estrogen receptor. Attenuation of Ca(2+) transients was mediated by estrogen action on VGCC. Nifedipine (10 microM), an L-type VGCC antagonist mimicked the effect of estrogen and when co-administered did not increase the estradiol inhibition of ATP-induced Ca(2+) transients. N- and P-type VGCC antagonists omega-conotoxin GVIA (1 microM) and omega-agatoxin IVA (100 nM), attenuated the ATP-induced Ca(2+) transients. Co-administration of these blockers with estrogen induced a further decrease of the ATP-induced Ca(2+) flux. Together, these results suggest that although ATP stimulation of P2X receptors activates L-, N-, and P-type VGCC, estradiol primarily blocks L-type VGCC. The estradiol regulation of this ATP-induced Ca(2+) transients suggests a mechanism through which estradiol may modulate nociceptive signaling in the peripheral nervous system.
雌激素与疼痛处理的调节有关。尽管这种调节发生在中枢神经系统内，但雌激素也可能作用于细胞体位于背根神经节（DRG）的初级传入神经元。用Fura-2加载大鼠DRG神经元的原代培养物，并通过荧光比率成像检测ATP诱导的细胞内钙浓度（Ca(2+)）变化。ATP是一种致痛剂，通过激活嘌呤能2X（P2X）型受体和电压门控钙通道（VGCC）诱导Ca(2+)变化。ATP（10 microM）在53%的中小DRG神经元中引起Ca(2+)瞬变增加（226.6±16.7 nM，n = 42）。与17β-雌二醇（100 nM）孵育5分钟可抑制85%的ATP反应性DRG神经元中ATP诱导的Ca(2+)（164±14.6 nM，P<0.05），而无活性的异构体17α-雌二醇则无作用。混合激动剂/拮抗剂他莫昔芬（1 microM）和特异性雌激素受体拮抗剂ICI 182780（1 microM）均阻断了雌二醇对ATP诱导的Ca(2+)瞬变的抑制作用。与牛血清白蛋白偶联的雌二醇不能穿过质膜，却能阻断ATP诱导的Ca(2+)，这表明雌二醇作用于膜相关雌激素受体。Ca(2+)瞬变的减弱是由雌激素对VGCC的作用介导的。L型VGCC拮抗剂硝苯地平（10 microM）模拟了雌激素的作用，共同给药时不会增加雌二醇对ATP诱导的Ca(2+)瞬变的抑制作用。N型和P型VGCC拮抗剂ω-芋螺毒素GVIA（1 microM）和ω-阿加毒素IVA（100 nM）可减弱ATP诱导的Ca(2+)瞬变。这些阻滞剂与雌激素共同给药可进一步降低ATP诱导的Ca(2+)通量。总之，这些结果表明，尽管ATP对P2X受体的刺激激活了L型、N型和P型VGCC，但雌二醇主要阻断L型VGCC。雌二醇对这种ATP诱导的Ca(2+)瞬变的调节提示了一种雌二醇可能在外周神经系统中调节伤害性信号传导的机制。
