SINGLE CYCLIC GMP-ACTIVATED CHANNEL ACTIVITY IN EXCISED PATCHES OF ROD OUTER SEGMENT MEMBRANE
SINGLE CYCLIC GMP-ACTIVATED CHANNEL ACTIVITY IN EXCISED PATCHES OF ROD OUTER SEGMENT MEMBRANE
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DOI：
10.1038/321066a0
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发表时间：
1986-05-01
期刊：
影响因子：
64.8
通讯作者：
YAU, KW
中科院分区：
文献类型：
--
作者：
HAYNES, LW;KAY, AR;YAU, KW
视网膜视杆外节的质膜含有环状 GMP 激活电导 1-6，这似乎是参与光转导的光敏电导 7。最近，发现这种电导在生理浓度下被 Mg2+（参考文献 3、8、9）和 Ca2+（参考文献 3、4、8-11）部分阻断，因此可能解释了在切除的膜片中缺乏可观察到的单通道活动1,3,8，以及从完整细胞的噪声测量中推导出的异常小的表观单位电导4,10,12,13。我们现在报道，正如这个想法所预期的那样，在没有二价阳离子的情况下，可以从切除的杆膜贴片中检测到单个 cGMP 激活的通道活性。最突出的单一电流的平均电导为~25 pS。观察到单独的通道开放（平均开放时间〜1毫秒）和开放的短突发（平均突发持续时间约为几毫秒）。此外，还有一些较小的事件可能代表其他电导状态。平均电流随 cGMP 浓度的三次方增加，表明通道分子上至少存在三个 cGMP 结合位点。在含有 cGMP 的溶液中加入 0.2 mM Mg2+ 后，观察到开放通道出现闪烁的堵塞现象； Ca2+的作用相似。结果证明光敏电导是水孔而不是载体，从而解决了有关光敏电导的难题。
The plasma membrane of retinal rod outer segments contains a cyclic GMP-activated conductance1–6which appears to be the light-sensitive conductance involved in phototransduction7. Recently, it has been found that this conductance is partially blocked by Mg2+(refs 3, 8, 9) and Ca2+(refs 3, 4, 8–11) at physiological concentrations, thus possibly accounting for the absence of observable single-channel activity in excised membrane patches1,3,8and for the unusually small apparent unit conductance deduced from noise measurements on intact cells4,10,12,13. We now report that, as expected from this idea, single cGMP-activated channel activity can be detected from an excised rod membrane patch in the absence of divalent cations. The most prominent unitary current had a mean conductance of ∼25 pS. Both individual channel openings (mean open time ∼1 ms) and short bursts of openings (mean burst duration of about a few milliseconds) were observed. In addition, there were smaller events which probably represented other states of the conductance. The mean current increased with the third power of cGMP concentration, suggesting that there are at least three cGMP-binding sites on the channel molecule. With 0.2 mM Mg2+in the cGMP-containing solution, a flickering block of the open channel was observed; the effect of Ca2+was similar. The results resolve a puzzle about the light-sensitive conductance by demonstrating that it is an aqueous pore rather than a carrier.