Covernton P J, Connolly J G
Department of Physiology and Pharmacology, University of Strathclyde, 27 Taylor Street, S.I.B.S., Glasgow, UK.
J Neurosci Methods. 2000 Mar 1;96(1):63-70. doi: 10.1016/s0165-0270(99)00185-5.
Assessing the potential of nicotinic agonists as therapeutic agents has frequently relied upon single component EC(50) values obtained from studies of nicotinic receptors expressed in Xenopus oocytes. We have evaluated the validity of this approach using voltage clamp techniques. In general, agonist concentration-response plots for the alpha3beta2, alpha3beta4, alpha4-1beta2, alpha4-1beta4 and alpha7 combinations were poorly fitted by a single component Hill-equation. Improved fits were obtained with the sum of two components, although only in the case of alpha3beta4 and alpha4-1beta2 was the improvement significant regardless of the weighting method used. For the acetylcholine (ACh) concentration-response relationships of the alpha4-1beta2 combination, the two EC(50) values were 0.3 and 58.3 microM. For the alpha3beta4 combination, the two EC(50) components were 39 and 2919 microM. The 39 microM component of alpha3beta4 represented 36% of the sum of the maximum responses of both curves. This shows that for some combinations, the secondary components represent a well-separated, major population of receptors. Therefore, published EC(50) values which assume that only a single subtype of functional receptor is present may not accurately describe agonist action may therefore need to be re-evaluated.
评估烟碱样激动剂作为治疗药物的潜力，常常依赖于从非洲爪蟾卵母细胞中表达的烟碱样受体研究获得的单一组分半数有效浓度（EC50）值。我们使用电压钳技术评估了这种方法的有效性。一般来说，α3β2、α3β4、α4 - 1β2、α4 - 1β4和α7组合的激动剂浓度 - 反应曲线，用单一组分的希尔方程拟合效果不佳。用两个组分的总和能得到更好的拟合，不过只有在α3β4和α4 - 1β2的情况下，无论使用何种加权方法，拟合的改善都很显著。对于α4 - 1β2组合的乙酰胆碱（ACh）浓度 - 反应关系，两个EC50值分别为0.3和58.3微摩尔。对于α3β4组合，两个EC50组分分别为39和2919微摩尔。α3β4的39微摩尔组分占两条曲线最大反应总和的36%。这表明对于某些组合，次要组分代表了一个分离良好的主要受体群体。因此，已发表的假设仅存在单一功能受体亚型的EC50值可能无法准确描述激动剂作用，可能因此需要重新评估。
