Fraser D D, MacVicar B A
Neuroscience Research Group, Faculty of Medicine, University of Calgary, Alberta, Canada.
J Neurosci. 1996 Jul 1;16(13):4113-28. doi: 10.1523/JNEUROSCI.16-13-04113.1996.
Cholinergic stimulation of the hippocampal formation results in excitation and/or seizure. We report here, using whole-cell patch-clamp techniques in the hippocampal slice (34-35 degrees C), a cholinergic-dependent slow afterdepolarization (sADP) and long-lasting plateau potential (PP). In the presence of 20 microM carbachol, action potential firing evoked by weak intracellular current injection elicited an sADP that lasted several seconds. Increased spike firing evoked by stronger depolarizing stimuli resulted in long-duration PPs maintained close to -20 mV. Removal of either Na+ or Ca2+ from the external media, intracellular Ca2+ ([Ca2+]i) chelation with 10 mM bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid, or the addition of 100 microM Cd2+ to the perfusate abolished both the sADP and PP. The sADP was depressed and the PP was abolished by either 10 microM nimodipine or 1 microM omega-conotoxin, whereas 1.2 microM tetrodotoxin was ineffective. The involvement of a Na+/Ca2+ exchanger was minimal because both the sADP and PP persisted after equimolar substitution of 50 mM Li+ for Na+ in the external media or reduction of the bath temperature to 25 degrees C. Finally in the absence of carbachol the sADP and PP could not be evoked when K+ channels were suppressed, suggesting that depression of K+ conductances alone was not sufficient to unmask the conductance. Based on these data, we propose that a Ca2+-activated nonselective cation conductance was directly enhanced by muscarinic stimulation. The sADP, therefore, represents activation of this conductance by residual [Ca2+]i, whereas the PP represents a novel regenerative event involving the interplay between high-voltage-activated Ca2+ channels and the Ca2+-activated nonselective cation conductance. This latter mechanism may contribute significantly to ictal depolarizations observed during cholinergic-induced seizures.
海马结构的胆碱能刺激会导致兴奋和/或癫痫发作。我们在此报告，利用海马脑片（34 - 35摄氏度）中的全细胞膜片钳技术，发现了一种胆碱能依赖性慢后去极化（sADP）和持久的平台电位（PP）。在存在20微摩尔卡巴胆碱的情况下，由弱细胞内电流注入诱发的动作电位发放会引发持续数秒的sADP。更强的去极化刺激诱发的锋电位发放增加会导致持续时间较长的PP，维持在接近 -20毫伏的水平。从细胞外液中去除Na⁺或Ca²⁺、用10毫摩尔双（2 - 氨基苯氧基）乙烷 - N，N，N'，N' - 四乙酸螯合细胞内Ca²⁺（[Ca²⁺]i），或向灌流液中添加100微摩尔Cd²⁺，均可消除sADP和PP。10微摩尔尼莫地平或1微摩尔ω - 芋螺毒素可使sADP减弱且PP消失，而1.2微摩尔河豚毒素则无效。Na⁺/Ca²⁺交换体的参与程度极小，因为在细胞外液中用50毫摩尔Li⁺等摩尔替代Na⁺或将浴温降至25摄氏度后，sADP和PP仍然存在。最后，在没有卡巴胆碱的情况下，当K⁺通道被抑制时无法诱发sADP和PP，这表明仅K⁺电导的降低不足以揭示该电导。基于这些数据，我们提出毒蕈碱刺激直接增强了一种Ca²⁺激活的非选择性阳离子电导。因此，sADP代表由残余[Ca²⁺]i激活该电导，而PP代表一种涉及高电压激活Ca²⁺通道与Ca²⁺激活的非选择性阳离子电导相互作用的新型再生事件。后一种机制可能对胆碱能诱发癫痫发作期间观察到的发作性去极化有显著贡献。
