Braun A P
Department of Pharmacology and Therapeutics, University of Calgary, AB, Canada.
Can J Physiol Pharmacol. 2001 Nov;79(11):919-23.
We observed that the current amplitude and activation of expressed, mouse brain large conductance, calcium-sensitive K+ channels (BKCa channels) may be reversibly enhanced following addition of low concentrations of the weakly permeant cation NH4+ to the cytoplasmic face of the channel in excised, inside-out membrane patches from HEK 293 cells. Conductance-voltage relations were left-shifted along the voltage axis by addition of NH4Cl in a concentration-dependent manner, with an EC50 of 18.5 mM. Furthermore, this effect was observed in the presence of cytosolic free calcium (approximately 1 microM), but was absent in a cytosolic bath solution containing nominally zero free calcium (e.g.. 5 mM EGTA only), a condition under which these channels undergo largely voltage-dependent gating. Recordings of single BKCa channel events indicated that NH4+ increased the channel open probability of single channel activity approximately 3-fold, but did not alter the amplitude of single channel currents. These findings suggest that the calcium-sensitive gating of mammalian BKCa channels may be modified by other ions present in cytosolic solution.
我们观察到，在从HEK 293细胞切下的内面向外膜片中，向通道胞质面添加低浓度的弱渗透性阳离子NH₄⁺后，表达的小鼠脑大电导钙敏感钾通道（BKCa通道）的电流幅度和激活可能会可逆增强。添加NH₄Cl后，电导-电压关系沿电压轴以浓度依赖的方式向左移动，EC₅₀为18.5 mM。此外，在胞质游离钙（约1 μM）存在的情况下观察到了这种效应，但在含有名义上零游离钙的胞质浴溶液（例如仅5 mM EGTA）中则不存在这种效应，在这种条件下这些通道主要经历电压依赖性门控。单个BKCa通道事件的记录表明，NH₄⁺使单通道活动的通道开放概率增加了约3倍，但未改变单通道电流的幅度。这些发现表明，哺乳动物BKCa通道的钙敏感门控可能会被胞质溶液中存在的其他离子所改变。
