Kardos J, Cash D J
Central Research Institute for Chemistry, Hungarian Academy of Sciences, Budapest.
J Neurochem. 1990 Oct;55(4):1095-9. doi: 10.1111/j.1471-4159.1990.tb03110.x.
Some data on the concentration range of response and the concentration for half-response (EC50) of gamma-aminobutyric acid (GABA) for the GABAA receptor are reviewed and compared. An analysis of the 36Cl- flux assay demonstrates that both the EC50 and the slope of a Hill plot depend on the ion influx or efflux assay time. The effects of depletion of the 36Cl- concentration gradient during the assay and of receptor desensitization on the result for a range of assay times are considered. The EC50 can be decreased by orders of magnitude by increasing the assay time. The EC50 measured in a finite time is less than the half-response concentration for the response(s) of the receptor. The extent of this difference depends on the receptor concentration per internal volume. The maximal decrease of EC50 depends on the rate of receptor desensitization. The computer simulations showed that a GABAA receptor with a half-response concentration of 100 microM GABA can give 36Cl- flux measurements with an EC50 value 100-fold lower.
本文回顾并比较了一些关于γ-氨基丁酸（GABA）对GABAA受体的反应浓度范围和半反应浓度（EC50）的数据。对36Cl-通量测定的分析表明，EC50和希尔图的斜率均取决于离子流入或流出测定时间。文中考虑了测定过程中36Cl-浓度梯度的耗竭以及受体脱敏对一系列测定时间结果的影响。通过增加测定时间，EC50可降低几个数量级。在有限时间内测得的EC50低于受体反应的半反应浓度。这种差异的程度取决于每单位内部体积的受体浓度。EC50的最大降低取决于受体脱敏速率。计算机模拟显示，半反应浓度为100μM GABA的GABAA受体可使36Cl-通量测量的EC50值降低100倍。
