Alvado Ludovic, Allen Charles N
Center for Research on Occupational and Environmental Toxicology, Oregon Health & Sciences University, Portland, OR 97239-3098, USA.
Brain Res. 2008 Jul 24;1221:24-9. doi: 10.1016/j.brainres.2008.05.025. Epub 2008 May 20.
Identifying the mechanisms that drive suprachiasmatic nucleus (SCN) neurons to fire action potentials with a higher frequency during the day than during the night is an important goal of circadian neurobiology. Selective chemical tools with defined mechanisms of action on specific ion channels are required for successful completion of these studies. The transient K(+) current (I(A)) plays an active role in neuronal action potential firing and may contribute to modulating the circadian firing frequency. Tetraethylammonium (TEA) is frequently used to inhibit delayed rectifier K(+) currents (I(DR)) during electrophysiological recordings of I(A). Depolarizing voltage-clamped hamster SCN neurons from a hyperpolarized holding potential activated both I(A) and I(DR). Holding the membrane potential at depolarized values inactivated I(A) and only the I(DR) was activated during a voltage step. The identity of I(A) was confirmed by applying 4-aminopyridine (5 mM), which significantly inhibited I(A). Reducing the TEA concentration from 40 mM to 1 mM significantly decreased the I(A) inactivation time constant (tau(inact)) from 9.8+/-3.0 ms to 4.9+/-1.2 ms. The changes in I(A)tau(inact) were unlikely to be due to a surface charge effect. The I(A) amplitude was not affected by TEA at any concentration or membrane potential. The isosmotic replacement of NaCl with choline chloride had no effect in I(A) kinetics demonstrating that the TEA effects were not due to a reduction of extracellular NaCl. We conclude that TEA modulates, in a concentration dependent manner, tau(inact) but not I(A) amplitude in hamster SCN neurons.
确定驱动视交叉上核（SCN）神经元在白天比夜间以更高频率发放动作电位的机制是昼夜节律神经生物学的一个重要目标。成功完成这些研究需要对特定离子通道具有明确作用机制的选择性化学工具。瞬时钾离子电流（I(A)）在神经元动作电位发放中起积极作用，可能有助于调节昼夜节律发放频率。在I(A)的电生理记录过程中，四乙铵（TEA）常用于抑制延迟整流钾离子电流（I(DR)）。将膜片钳制的仓鼠SCN神经元从超极化的钳制电位去极化，可激活I(A)和I(DR)。将膜电位保持在去极化值会使I(A)失活，在电压阶跃期间仅激活I(DR)。通过应用4-氨基吡啶（5 mM）证实了I(A)的特性，其显著抑制了I(A)。将TEA浓度从40 mM降低到1 mM，可使I(A)失活时间常数（tau(inact)）从9.8±3.0 ms显著降低到4.9±1.2 ms。I(A) tau(inact)的变化不太可能是由于表面电荷效应。I(A)的幅度在任何浓度或膜电位下均不受TEA影响。用氯化胆碱等渗替代氯化钠对I(A)动力学没有影响，表明TEA的作用不是由于细胞外氯化钠的减少。我们得出结论，TEA以浓度依赖的方式调节仓鼠SCN神经元中的tau(inact)，但不影响I(A)的幅度。
