McLatchie L M, Matthews H R
Physiological Laboratory, University of Cambridge, U.K.
Proc Biol Sci. 1994 Mar 22;255(1344):231-6. doi: 10.1098/rspb.1994.0033.
Block by L-cis-diltiazem and amiloride of the cyclic GMP-activated conductance was studied in inside-out patches excised from the salamander rod outer segment. When cytoplasmic pH was varied, the steady-state level of block by L-cis-diltiazem changed in the way that would be predicted if it were the protonated ammonium group that is responsible for effecting block. This is in contrast to the recent results of Haynes (J. gen. Physiol. 100, 783 (1992)) in catfish cones, where no such change was seen. Amiloride was found to block the conductance with a similar voltage dependence to that of L-cis-diltiazem. The dependence of amiloride block on cytoplasmic pH was found to be shifted relative to that of L-cis-diltiazem, consistent with the 1 pH-unit higher pKa value of amiloride and the idea that it is only the charged form of amiloride which can effect block. This suggests that the results seen with L-cis-diltiazem were indeed due to changes in the proportion of blocker in the protonated form, and not to effects of protons on the channel.
在从蝾螈视杆外段分离的内面向外膜片中研究了L-顺式地尔硫䓬和氨氯地平对环鸟苷酸激活的电导的阻断作用。当细胞质pH发生变化时，L-顺式地尔硫䓬的稳态阻断水平的变化方式符合如下预测：即如果是质子化的铵基团负责产生阻断作用的话，就会出现这种变化。这与海恩斯（《普通生理学杂志》100, 783 (1992)）最近在鲶鱼视锥细胞中得到的结果相反，在鲶鱼视锥细胞中未观察到这种变化。发现氨氯地平阻断电导的电压依赖性与L-顺式地尔硫䓬相似。发现氨氯地平阻断作用对细胞质pH的依赖性相对于L-顺式地尔硫䓬发生了偏移，这与氨氯地平的pKa值高1个pH单位以及只有氨氯地平的带电形式才能产生阻断作用的观点一致。这表明L-顺式地尔硫䓬的实验结果确实是由于质子化形式的阻断剂比例发生了变化，而不是质子对通道的影响。
