Nishizaki T, Matsuoka T, Nomura T, Sumikawa K
Department of Physiology, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
Brain Res Mol Brain Res. 1998 Jun 1;57(1):173-9. doi: 10.1016/s0169-328x(98)00091-6.
The present study investigated the effects of arachidonic acid on Torpedo (alpha beta gamma delta) and neuronal nicotinic acetylcholine (ACh) receptors (chick alpha7; rat alpha7, alpha3 beta2, alpha3 beta4, alpha4 beta2, and alpha4 beta4). Arachidonic acid (10 microM) depressed currents through normal Torpedo ACh receptors during treatment and afterward, persistently (>/=30 min) potentiated the currents. The potentiation was blocked by the selective protein kinase C (PKC) inhibitor, GF109203X or PKC inhibitor peptide (PKCI). The depression was not inhibited by any protein kinase inhibitor examined here, but greater in Ca2+-free extracellular solution. Arachidonic acid also potentiated currents through mutant Torpedo ACh receptors lacking PKC phosphorylation sites at Ser333 on the alpha subunit and Ser377 on the delta subunit without depression, but otherwise, it depressed currents through mutant receptors replacing of each Ser by negatively charged amino acid residue, possibly that mimics PKC phosphorylation of the receptors. These results suggest that the depression was due to the direct blocking effect on Ca2+-modulatory sites, which was accelerated under conditions of the receptors phosphorylated by PKC, and that the potentiation was caused by PKC activation, independently of PKC phosphorylation of the receptors. Arachidonic acid reduced currents through chick alpha7 receptors by a mechanism independent of protein kinase activation. In contrast, arachidonic acid potentiated currents through rat alpha7, alpha3 beta2, alpha4 beta2, and alpha4 beta4 receptors, perhaps by the same mechanism as the potentiation observed in Torpedo ACh receptors, although it had no effect on rat alpha3 beta4 receptors. The results of the present study thus demonstrate that arachidonic acid exerts diverse actions on nicotinic ACh receptors by different mechanisms.
本研究调查了花生四烯酸对电鳐（αβγδ）和神经元烟碱型乙酰胆碱（ACh）受体（鸡α7；大鼠α7、α3β2、α3β4、α4β2和α4β4）的影响。花生四烯酸（10微摩尔）在处理过程中使通过正常电鳐ACh受体的电流降低，处理后持续（≥30分钟）增强电流。这种增强被选择性蛋白激酶C（PKC）抑制剂GF109203X或PKC抑制剂肽（PKCI）阻断。这里检测的任何蛋白激酶抑制剂均未抑制电流降低，但在无钙细胞外溶液中降低作用更强。花生四烯酸还增强了通过α亚基上Ser333和δ亚基上Ser377缺乏PKC磷酸化位点的突变型电鳐ACh受体的电流，且无电流降低现象，但除此之外，它使通过将每个Ser替换为带负电荷氨基酸残基的突变型受体的电流降低，这可能模拟了受体的PKC磷酸化。这些结果表明，电流降低是由于对Ca2+调节位点的直接阻断作用，在受体被PKC磷酸化的条件下这种作用加速，而电流增强是由PKC激活引起的，与受体的PKC磷酸化无关。花生四烯酸通过一种独立于蛋白激酶激活的机制降低通过鸡α7受体的电流。相比之下，花生四烯酸增强了通过大鼠α7、α3β2、α4β2和α4β4受体的电流，可能与在电鳐ACh受体中观察到的增强机制相同，尽管它对大鼠α3β4受体没有影响。因此，本研究结果表明花生四烯酸通过不同机制对烟碱型ACh受体发挥多种作用。
