Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO 63110, USA.
Br J Pharmacol. 2010 Aug;160(8):1906-15. doi: 10.1111/j.1476-5381.2010.00761.x.
A fundamental property of transmitter-gated ion channels is the probability a channel will be open (P(open)) when stimulated by a concentration of agonist that elicits a maximal response. This value is critical for interpreting steady-state concentration-response relationships in terms of channel activation, and for understanding the actions of drugs that potentiate responses. We used analysis of non-stationary noise to estimate the maximal probability the nicotinic alpha4beta2 receptor is open.
HEK293 cells stably transfected to express human alpha4beta2 nicotinic receptors were studied using whole-cell voltage clamp. Nicotinic agonists (acetylcholine, nicotine, cytisine and 5-iodo A-85380) were applied, and the relationship between variance of the elicited whole-cell current and mean current was analysed.
The variance did not increase linearly with the mean current. For acetylcholine and nicotine the relationship between variance and mean indicates that the maximal P(open) is greater than 0.8. The number of agonist-activatable channels was estimated to be about 1000 per cell. The mean single channel conductance at -60 mV was indistinguishable when currents were elicited by acetylcholine (18 pS), nicotine (17 pS) or 5-iodo A-85380 (17 pS), whereas the value for cytisine was larger (24 pS).
The neuronal nicotinic alpha4beta2 receptor has a maximal probability of being open that is greater than 0.8. This conclusion applies to the receptor containing three alpha4 and two beta2 subunits (the low-sensitivity stoichiometry), but may not apply to the receptor containing two alpha4 and three beta2 subunits (the high-sensitivity stoichiometry).
递质门控离子通道的一个基本特性是，当受到引发最大反应的激动剂浓度刺激时，通道开放的概率（P（open））。该值对于根据通道激活来解释稳态浓度-反应关系以及理解增强反应的药物的作用至关重要。我们使用非稳态噪声分析来估计烟碱型α4β2 受体的最大开放概率。
使用全细胞膜片钳技术研究稳定转染人α4β2 烟碱受体的 HEK293 细胞。应用烟碱激动剂（乙酰胆碱、尼古丁、烟碱和 5-碘代 A-85380），并分析诱发全细胞电流的方差与平均电流之间的关系。
方差与平均电流之间的关系并非线性增加。对于乙酰胆碱和尼古丁，方差与平均电流之间的关系表明最大 P（open）大于 0.8。每个细胞中估计有大约 1000 个可被激动剂激活的通道。在 -60 mV 下，电流由乙酰胆碱（18 pS）、尼古丁（17 pS）或 5-碘代 A-85380（17 pS）引发时，单通道电导的平均值没有区别，而烟碱的数值较大（24 pS）。
神经元烟碱型α4β2 受体的最大开放概率大于 0.8。这一结论适用于含有三个α4 和两个β2 亚基的受体（低敏感性计量比），但可能不适用于含有两个α4 和三个β2 亚基的受体（高敏感性计量比）。
