Responses of rat P2X2 receptors to ultrashort pulses of ATP provide insights into ATP binding and channel gating.
Responses of rat P2X2 receptors to ultrashort pulses of ATP provide insights into ATP binding and channel gating.
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DOI：
10.1085/jgp.200709779
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发表时间：
2007-08
期刊：
影响因子：
--
通讯作者：
Hume RI
中科院分区：
文献类型：
--
作者：
Moffatt L;Hume RI
为了深入了解位于突触的P2X2受体可能发挥作用的方式，我们探索了包含许多这些通道的外向补丁的特性，因为ATP非常迅速地应用和去除。使用一种新的方法来校准溶液在完整贴片上的交换速度，我们能够可靠地产生持续<200 μs的ATP应用。对于所有浓度的ATP，在ATP到达受体和第一个可检测到的内向电流之间至少有80 μs的延迟。在200 μs的ATP脉冲下，电流上升相的时间常数约为600 μs。因此，大多数通道开放发生在没有游离ATP存在时。电流失活的时间常数为0.60 ms。的峰值响应的幅度的一个短暂的脉冲的饱和浓度的ATP是在一个长期的应用程序中获得的相同浓度的ATP的0.70%。因此，ATP离开完全配体化的通道，至少30%的时间不产生开放。广泛的动力学模型显示，三种不同的方案，适合的数据，顺序模型和两个变构模型。考虑到ATP饱和时的开启延迟，有必要将中间关闭状态纳入所有三种方案。这些动力学性质表明，在使用同型P2X2受体的突触处对ATP的反应预计将大大超过由单个突触前锋电位产生的突触ATP瞬变的持续时间。像NMDA受体一样，P2X2受体在数百毫秒的时间尺度上提供了突触整合的复杂模式的潜力。
To gain insight into the way that P2X2 receptors localized at synapses might function, we explored the properties of outside-out patches containing many of these channels as ATP was very rapidly applied and removed. Using a new method to calibrate the speed of exchange of solution over intact patches, we were able to reliably produce applications of ATP lasting <200 μs. For all concentrations of ATP, there was a delay of at least 80 μs between the time when ATP arrived at the receptor and the first detectable flow of inward current. In response to 200-μs pulses of ATP, the time constant of the rising phase of the current was ∼600 μs. Thus, most channel openings occurred when no free ATP was present. The current deactivated with a time constant of ∼60 ms. The amplitude of the peak response to a brief pulse of a saturating concentration of ATP was ∼70% of that obtained during a long application of the same concentration of ATP. Thus, ATP leaves fully liganded channels without producing an opening at least 30% of the time. Extensive kinetic modeling revealed three different schemes that fit the data well, a sequential model and two allosteric models. To account for the delay in opening at saturating ATP, it was necessary to incorporate an intermediate closed state into all three schemes. These kinetic properties indicate that responses to ATP at synapses that use homomeric P2X2 receptors would be expected to greatly outlast the duration of the synaptic ATP transient produced by a single presynaptic spike. Like NMDA receptors, P2X2 receptors provide the potential for complex patterns of synaptic integration over a time scale of hundreds of milliseconds.
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