Solute inaccessible aqueous volume changes during opening of the potassium channel of the squid giant axon.
Solute inaccessible aqueous volume changes during opening of the potassium channel of the squid giant axon.
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DOI：
10.1016/s0006-3495(90)82623-0
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发表时间：
1990-05
影响因子：
3.4
通讯作者：
J. Zimmerberg;F. Bezanilla;V. Parsegian
中科院分区：
文献类型：
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作者：
J. Zimmerberg;F. Bezanilla;V. Parsegian
我们将不同渗透压的溶液对称地应用于灌注的ttx处理的巨大轴突的内外。钾电导G随渗透胁迫的增加而减小，但对电压-电流曲线的形状和位置没有影响。必须区分渗透剂的三种可能作用：渗透应力、通道阻塞和降低溶液导电性。为此，我们比较了使用(a)相同渗透应力、(b)相同电导率或(c)相同阻断剂的内外部溶液对得到的结果。不同胁迫种类（山梨醇或蔗糖）对G的影响相同；这为反对阻塞机制提供了一些证据。外溶液的电导率对K电流的影响较小；内溶液电导率为零。施旺电池层串联电阻的变化可以解释外溶液电导率的小影响。因此，G抑制的主要原因似乎是施加的渗透胁迫。利用这一结果，我们开发了一些模型，其中通道在电压控制但渗透不敏感的关闭状态和电压无关但渗透敏感的关闭/打开步骤之间进行过渡。我们假定这种开态的电导不随渗透应力的变化而变化。通过这种方式，我们估计，当鱿鱼轴突的平均延迟整流钾通道打开时，额外的1,350 +/- 200 A3或40-50个溶质不可接近的水分子似乎与之相关。
We have applied solutions with varying osmotic pressures symmetrically to the inside and outside of perfused, TTX-treated, giant axons. The potassium conductance G decreased with increasing osmotic stress, but there was no effect on either the shape or the position of the voltage-current curve. One must distinguish three possible actions of the osmotic agent: osmotic stress, channel blocking, and lowered solution conductivity. To do so, we compared results obtained working with pairs of internal and external solutions of either (a) equal osmotic stress, (b) equal conductivity, or (c) the same blocking agent. There was the same change in G irrespective of the type of stressing species (sorbitol or sucrose); this provides some evidence against a blocking mechanism. The conductivity of the external solution had a small effect on K currents; internal solution conductivity had none. A change in series resistance of the Schwann cell layer could account for the small effect of external solution conductivity. The primary cause of G depression appears, then, to be the applied osmotic stress. Using this result, we have developed models in which the channel has a transition between closed states under voltage control but osmotically insensitive and a closed/open step that is voltage-independent but osmotically sensitive. We have assumed that the conductance of this open state does not change with osmotic stress. In this way, we estimate that an additional 1,350 +/- 200 A3 or 40–50 molecules of solute-inaccessible water appear to associate with the average delayed rectifier potassium channel of the squid axon when it opens.