Shirasaki T, Houtani T, Sugimoto T, Matsuda H
Department of Physiology, Kansai Medical University, Moriguchi, 570-8506, Osaka, Japan.
Brain Res. 2001 Nov 2;917(2):191-205. doi: 10.1016/s0006-8993(01)02916-x.
Spontaneous transient outward currents have been found in peripheral neurons and smooth muscle cells, but rarely in central neurons. Using a nystatin-perforated patch clamp technique, we succeeded in recording spontaneous transient outward currents in mouse dentate gyrus granule cells. Nociceptin/orphanin FQ increased the amplitude and frequency of transient outward currents. We consider modulation of spontaneous transient outward currents to be a new means to regulate cell activity in central neurons, and studied their characteristics and mechanism of augmentation. The whole-cell current-voltage relationship showed outward rectification and the reversal potential was close to the equilibrium potential for K+. The frequency of spontaneous transient outward currents increased at depolarized potentials. Tetraethylammonium, iberiotoxin and a Ca2+ chelator BAPTA-AM inhibited spontaneous transient outward currents. These results suggest the involvement of large-conductance Ca2+-activated K+ channels. Single-channel recordings in the inside-out configuration revealed Ca2+-activated K+ channels with a conductance ranging from 82 to 352 pS. The augmenting effect of nociceptin/orphanin FQ was cancelled by [Phe1psi(CH2-NH)Gly2]Nociceptin(1-13)NH2. Cd2+ did not affect the transient outward currents or augmentation by nociceptin/orphanin FQ. Whereas nociceptin/orphanin FQ, theophylline and cyclic ADP ribose induced transient outward currents with short duration observed under control conditions, inositol 1,4,5-trisphosphate induced transient outward currents with long duration, in addition to those with short duration. Ryanodine inhibited nociceptin/orphanin FQ from augmenting spontaneous transient outward currents. Our data suggest that Ca2+ sparks transiently activate large-conductance Ca2+-activated K+ channels to induce transient outward currents. Nociceptin/orphanin FQ probably sensitizes ryanodine receptors and increases transient outward currents to reduce cell excitability.
在外周神经元和平滑肌细胞中发现了自发瞬态外向电流，但在中枢神经元中很少见。我们采用制霉菌素穿孔膜片钳技术，成功记录到了小鼠齿状回颗粒细胞中的自发瞬态外向电流。孤啡肽增加了瞬态外向电流的幅度和频率。我们认为，自发瞬态外向电流的调制是调节中枢神经元细胞活动的一种新方式，并研究了其特征和增强机制。全细胞电流-电压关系呈外向整流，反转电位接近K+的平衡电位。自发瞬态外向电流的频率在去极化电位时增加。四乙铵、iberiotoxin和Ca2+螯合剂BAPTA-AM抑制自发瞬态外向电流。这些结果表明大电导Ca2+激活K+通道参与其中。内面向外模式的单通道记录显示，Ca2+激活K+通道的电导范围为82至352 pS。[Phe1psi(CH2-NH)Gly2]Nociceptin(1-13)NH2消除了孤啡肽的增强作用。Cd2+不影响瞬态外向电流或孤啡肽的增强作用。在对照条件下，孤啡肽、茶碱和环ADP核糖诱导的瞬态外向电流持续时间短，而肌醇1,4,5-三磷酸除了诱导持续时间短的瞬态外向电流外，还诱导持续时间长的瞬态外向电流。Ryanodine抑制孤啡肽增强自发瞬态外向电流。我们的数据表明，Ca2+火花短暂激活大电导Ca2+激活K+通道以诱导瞬态外向电流。孤啡肽可能使ryanodine受体敏感化并增加瞬态外向电流以降低细胞兴奋性。
