Salánki J, Evans M L, Carpenter D O
Wadsworth Center for Laboratories and Research, New York State Department of Health, University at Albany 12237.
Brain Res. 1989 Aug 28;495(2):298-308. doi: 10.1016/0006-8993(89)90222-9.
We have studied the process of acetylcholine receptor desensitization on Aplysia medial pleural neurons under voltage clamp conditions. Acetylcholine, applied by microperfusion, elicits a biphasic response on these neurons, a rapid component which reverses polarity at about -60 mV and is Cl-dependent, and a slower component which reverses at about -85 mV and is K-dependent. Both components show desensitization, and the present study focuses on the K-dependent component, which could be isolated by maintaining membrane potential at the Cl equilibrium potential or by blocking the Cl component pharmacologically. K-dependent acetylcholine responses on these neurons varied in regard to time to peak of response and rate of desensitization. While the rising phase of the response was always fitted by a single exponential process, times to peak were divided somewhat arbitrarily into three broad groups of fast (less than 3 s), medium (3-6 s) and slow (greater than 6 s). Desensitization of fast responses was best described by two exponential processes plus a constant, medium responses by a double exponential, and slow responses by single exponential plus a constant. The apparent dissociation constant of acetylcholine was 17.3 +/- 1.6 microM. The best fit of responses for a given cell remained constant over a range of acetylcholine doses, but the kinetics of both fast and slow components accelerated with dose and depolarization. The fast component of desensitization was very temperature dependent. In neurons where it was present it was abolished by cooling, while in neurons with no fast component at room temperature it would appear with warming. The time constant of the fast component varied inversely with temperature. The time constant of the slow component was maximal at 22-24 degrees C, and fell on either side of this temperature. These results suggest that receptor desensitization for acetylcholine K responses is, like Na-dependent responses, composed of two independent processes. When responses to the acetylcholine agonists, carbachol and arecoline, were compared to those of acetylcholine on fast-type neurons, the times to peak varied in the order acetylcholine less than carbachol less than arecoline. The carbachol response was best fitted by two exponential functions, while arecoline was best fitted by a single exponential plus a constant.
我们在电压钳制条件下研究了海兔内侧胸膜神经元上乙酰胆碱受体脱敏的过程。通过微量灌注施加的乙酰胆碱会在这些神经元上引发双相反应，一个快速成分在约 -60 mV 时极性反转且依赖于 Cl⁻，一个较慢成分在约 -85 mV 时反转且依赖于 K⁺。两个成分均表现出脱敏现象，本研究聚焦于依赖 K⁺的成分，该成分可通过将膜电位维持在 Cl⁻平衡电位或通过药理学方法阻断 Cl⁻成分来分离。这些神经元上依赖 K⁺的乙酰胆碱反应在反应峰值时间和脱敏速率方面存在差异。虽然反应的上升阶段总是由单个指数过程拟合，但峰值时间在某种程度上被任意分为快速（小于 3 秒）、中等（3 - 6 秒）和缓慢（大于 6 秒）三大类。快速反应的脱敏最好用两个指数过程加一个常数来描述，中等反应用双指数描述，缓慢反应用单指数加一个常数描述。乙酰胆碱的表观解离常数为 17.3 ± 1.6 μM。在一系列乙酰胆碱剂量范围内，给定细胞反应的最佳拟合保持不变，但快速和缓慢成分的动力学均随剂量和去极化而加速。脱敏的快速成分非常依赖温度。在存在该成分的神经元中，冷却可将其消除，而在室温下无快速成分的神经元中，升温时会出现该成分。快速成分的时间常数与温度成反比。缓慢成分的时间常数在 22 - 24℃时最大，在该温度两侧均下降。这些结果表明，乙酰胆碱 K⁺反应的受体脱敏与 Na⁺依赖反应一样，由两个独立过程组成。当将乙酰胆碱激动剂卡巴胆碱和槟榔碱对快速型神经元的反应与乙酰胆碱的反应进行比较时，峰值时间按乙酰胆碱＜卡巴胆碱＜槟榔碱的顺序变化。卡巴胆碱反应最好用两个指数函数拟合，而槟榔碱最好用单指数加一个常数拟合。
