Harmaline competitively inhibits [H-3]MK-801 binding to the NMDA receptor in rabbit brain
Harmaline competitively inhibits [H-3]MK-801 binding to the NMDA receptor in rabbit brain
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DOI：
10.1016/s0006-8993(97)00606-9
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发表时间：
1997-10-03
期刊：
影响因子：
2.9
通讯作者：
Harvey, JA
中科院分区：
文献类型：
--
作者：
Du, W;Aloyo, VJ;Harvey, JA
Harmaline是一种β-咔啉衍生物，已知通过直接激活下橄榄中的细胞来产生震颤。然而，harvesting作用的受体仍然未知。最近有报道称，非竞争性NMDA通道阻断剂MK-801可阻断哈氏剂的震颤作用。本研究检查了MK-801在家兔中对肝素作用的阻断是否是由于MK-801结合位点的药理学拮抗作用。这是通过测定来自含下橄榄核组织和大脑皮质的膜组分中的[H-3]MK-801结合来完成的。骆驼蓬碱完全取代饱和的[H-3]MK-801结合在下橄榄和皮质，表观IC 50值分别为60和170 μ M。这些IC 50值与产生震颤所需的高剂量的肝素一致，例如，10-30 mg/kg。[H-3]MK-801饱和实验的非线性曲线拟合分析表明，[H-3]MK-801与单个位点结合，并且如K-d而非B-max的偏移所示，[H-3]MK-801与NMDA受体结合的Harrene置换是竞争性的。此外，Schild图给出的斜率与1无显著差异，表明harvestin使[H-3]MK-801从其在NMDA阳离子通道内的结合位点置换，而不是通过对NMDA受体上谷氨酸或其他变构位点的作用。这些发现提供了体外证据，证明MK-801对骆驼蓬碱诱导的震颤的竞争性阻断发生在与NMDA受体偶联的钙通道内。我们的假设是，harvestin通过在MK-801结合位点作为反向激动剂，从而打开阳离子通道，从而产生震颤。(C)1997年Elsevier Science B.V.
Harmaline, a beta-carboline derivative, is known to produce tremor through a direct activation of cells in the inferior olive. However, the receptor(s) through which harmaline acts remains unknown. It was recently reported that the tremorogenic actions of harmaline could be blocked by the noncompetitive NMDA channel blocker, MK-801. This study examined whether the blockade of harmaline's action, in the rabbit, by MK-801 was due to a pharmacological antagonism at the MK-801 binding site. This was accomplished by measurement of [H-3]MK-801 binding in membrane fractions derived from tissue containing the inferior olivary nucleus and from cerebral cortex. Harmaline completely displaced saturable [H-3]MK-801 binding in both the inferior olive and cortex with apparent IC50 values of 60 and 170 mu M, respectively. These IC50 values art consistent with the high doses of harmaline required to produce tremor, e.g., 10-30 mg/kg. Non-linear curve fitting analysis of [H-3]MK-801 saturation experiments indicated that [H-3]MK-801 bound to a single site and that harmaline's displacement of [H-3]MK-801 binding to the NMDA receptor was competitive as indicated by a shift in K-d but not in B-max. In addition, a Schild plot gave a slope that was not significantly different from 1 indicating that harmaline was producing a displacement of [H-3]MK-801 from its binding site within the NMDA cation channel and not through an action at the glutamate or other allosteric sites on the NMDA receptor. These findings provide in vitro evidence that the competitive blockade of harmaline-induced tremor by MK-801 occurs within the calcium channel coupled to the NMDA receptor. Our hypothesis is that harmaline produces tremor by acting as an inverse agonist at the MK-801 binding site and thus opening the cation channel. (C) 1997 Elsevier Science B.V.