Martínez-Padrón M, Ferrús A
Instituto Cajal (Consejo Superior de Investigaciones Científicas), 28002 Madrid, Spain.
J Neurosci. 1997 May 15;17(10):3412-24. doi: 10.1523/JNEUROSCI.17-10-03412.1997.
We have performed direct electrophysiological recordings from Drosophila peptidergic synaptic boutons in situ, taking advantage of a mutation, ecdysone, which causes an increase in size of these terminals. Using patch-clamp techniques, we have analyzed voltage-dependent potassium currents at the macroscopic and single-channel level. The synaptic membrane contained at least two distinct voltage-activated potassium currents with different kinetics and voltage sensitivity: an IA-like current with fast activation and inactivation kinetics and voltage-dependent steady-state inactivation; a complex delayed current that includes a slowly inactivating component, resembling the IK described in other preparations; and a noninactivating component. The IA-like current in these peptidergic boutons is not encoded by the gene Shaker, because it is not affected by null mutations at this locus. Rather, synaptic IA has properties similar to those of the Shal-encoded IA. Single-channel recordings revealed the presence in synaptic membranes of three different potassium channel types (A2, KD, KL), with biophysical properties that could account for the macroscopic currents and resemble those of the Shal, Shab, and Shaw channels described in heterologous expression systems and Drosophila neuronal somata. A2 channels (6-9 pS) have brief open times, and like the macroscopic IA they exhibited voltage-dependent steady-state inactivation and a rapidly inactivating ensemble average current profile. KD channels (13-16 pS) had longer open times, activate and inactivate with much slower kinetics, and may account for the slowly inactivating component of the macroscopic current. KL (44-54 pS) channels produced a noninactivating ensemble average and may contribute to the delayed macroscopic current observed.
我们利用一种名为蜕皮激素的突变，该突变会导致果蝇肽能突触小体的大小增加，从而对原位果蝇肽能突触小体进行了直接电生理记录。使用膜片钳技术，我们在宏观和单通道水平上分析了电压依赖性钾电流。突触膜包含至少两种具有不同动力学和电压敏感性的不同电压激活钾电流：一种类似IA的电流，具有快速激活和失活动力学以及电压依赖性稳态失活；一种复杂的延迟电流，包括一个缓慢失活的成分，类似于其他制剂中描述的IK；以及一个非失活成分。这些肽能突触小体中的类似IA的电流不是由Shaker基因编码的，因为它不受该位点无效突变的影响。相反，突触IA具有与Shal编码的IA相似的特性。单通道记录揭示了突触膜中存在三种不同类型的钾通道（A2、KD、KL），其生物物理特性可以解释宏观电流，并且类似于在异源表达系统和果蝇神经元胞体中描述的Shal、Shab和Shaw通道。A2通道（6 - 9 pS）开放时间短暂，与宏观IA一样，它们表现出电压依赖性稳态失活和快速失活的总体平均电流曲线。KD通道（13 - 16 pS）开放时间更长，激活和失活的动力学要慢得多，可能解释了宏观电流的缓慢失活成分。KL（44 - 54 pS）通道产生非失活的总体平均电流，可能有助于观察到的延迟宏观电流。
