Ratner E, Tour O, Parnas H
The Otto Loewi Minerva Center for Cellular and Molecular Neurobiology and the Department of Neurobiology, the Hebrew University, Jerusalem 91904, Israel.
Biophys J. 2000 Feb;78(2):731-45. doi: 10.1016/S0006-3495(00)76631-8.
We propose a new method for calculating the number of agonist binding sites (n) in ligand-gated receptor channels from the initial phase of the current. This method is based on the fact that the relation between the current (I) and its first-time derivative (I') at the beginning of the current reflects the number of transitions that lead to channel opening. We show that, for constant agonist concentration, the above relationship at t --> 0 provides the number of steps leading to channel opening. When the agonist concentration is not constant but rather increases linearly with time, the corresponding value can be obtained using a slightly modified procedure. The analytical results were compared with computer simulations and a good match between the two was obtained. The theoretical procedure was then validated experimentally using the nicotinic receptor, because, for this receptor, the number of binding sites is well established. Indeed, the expected number of two binding sites was obtained. The method was then tested for the quisqualate-type glutamate receptor channel from the opener muscle of crayfish. The number of this receptor's binding sites is not fully resolved. Our results suggest that, for this glutamate receptor as well, two binding sites must be occupied to open the channel.
我们提出了一种新方法，可根据电流的初始阶段计算配体门控受体通道中激动剂结合位点的数量（n）。该方法基于这样一个事实，即电流开始时电流（I）与其一阶导数（I'）之间的关系反映了导致通道开放的转变数量。我们表明，对于恒定的激动剂浓度，t→0时的上述关系给出了导致通道开放的步骤数。当激动剂浓度不是恒定的，而是随时间线性增加时，可以使用略有修改的程序获得相应的值。将分析结果与计算机模拟进行了比较，两者之间取得了很好的匹配。然后使用烟碱样受体对理论程序进行了实验验证，因为对于该受体，结合位点的数量已得到充分确定。实际上，获得了预期的两个结合位点的数量。然后对小龙虾 opener 肌肉中的 quisqualate 型谷氨酸受体通道进行了该方法的测试。该受体结合位点的数量尚未完全确定。我们的结果表明，对于这种谷氨酸受体，也必须占据两个结合位点才能打开通道。
