Guo Xiaochuan, Lester Robin A J
Department of Neurobiology, McKnight Brain Institute, University of Alabama at Birmingham, 1825 University Boulevard, Birmingham AL 35294-2182, USA.
J Neurophysiol. 2007 Jan;97(1):93-101. doi: 10.1152/jn.01047.2005. Epub 2006 Oct 18.
The relationship between the concentration of intracellular Ca2+ (Ca2+) and recovery from desensitization of nicotinic acetylcholine receptors (nAChRs) in rat medial habenula (MHb) neurons was investigated using the whole cell patch-clamp techniques in combination with microfluorescent Ca2+ measurements. Recovery from desensitization was assessed with a paired-pulse agonist application protocol. Application of 100 microM nicotine (5 s) caused pronounced desensitization of nAChRs, after which recovery proceeded with two components. The relative weight of the two phases of recovery was sensitive to the nature of the intracellular Ca2+ chelator, with a greater fraction of channels recovering during the fast phase in the presence of BAPTA than EGTA. Recovery was affected by differential Ca2+ buffering only when Ca2+ was present in the extracellular solution, implying that Ca2+ influx through nAChRs was responsible for slowing the recovery. Simultaneous Ca2+ measurements showed that recovery from desensitization was inversely correlated with the instantaneous Ca2+, further supporting the suggestion that elevation of Ca2+ limits the return of nAChRs to the resting state. In a separate set of experiments, activation of voltage-gated Ca2+ channels during the recovery phase produced a sufficiently large increase in Ca2+ to reduce recovery from desensitization even in the absence of Ca2+ influx through nAChRs. Overall, it is suggested that Ca2+ entry through both nAChRs and voltage-gated Ca2+ channels exerts a negative feedback on nAChR activity through stabilization of desensitized states. The interaction of these two Ca2+ sources could form the basis of a coincidence detector under specific circumstances.
运用全细胞膜片钳技术并结合微荧光法测量细胞内钙离子浓度（Ca2+），研究了大鼠内侧缰核（MHb）神经元中细胞内Ca2+浓度（Ca2+）与烟碱型乙酰胆碱受体（nAChRs）脱敏恢复之间的关系。采用配对脉冲激动剂应用方案评估脱敏恢复情况。施加100 microM尼古丁（5秒）可使nAChRs明显脱敏，之后恢复过程呈现两个阶段。恢复的两个阶段的相对权重对细胞内Ca2+螯合剂的性质敏感，在存在BAPTA的情况下，快速阶段恢复的通道比例比EGTA存在时更大。仅当细胞外溶液中存在Ca2+时，恢复才受不同Ca2+缓冲的影响，这意味着通过nAChRs的Ca2+内流是恢复减慢的原因。同时进行的Ca2+测量表明，脱敏恢复与瞬时Ca2+呈负相关，进一步支持了Ca2+升高会限制nAChRs恢复到静息状态的观点。在另一组实验中，恢复阶段电压门控Ca2+通道的激活使Ca2+有足够大的增加，即使在没有通过nAChRs的Ca2+内流的情况下，也能减少脱敏恢复。总体而言，提示通过nAChRs和电压门控Ca2+通道的Ca2+内流通过稳定脱敏状态对nAChR活性施加负反馈。在特定情况下，这两种Ca2+来源的相互作用可能构成巧合探测器的基础。
