Granitzer M, Mountian I, Van Driessche W
Laboratory of Physiology, KU Leuven, Gasthuisberg, Belgium.
Pflugers Arch. 1995 Aug;430(4):493-500. doi: 10.1007/BF00373885.
The association (ON) and dissociation (OFF) rates of either positively charged amiloride or its uncharged analogue, CDPC (6-chloro-3, 5-diaminopyrazine-2-carboxamide), with the apical Na+ channel protein of renal A6 cells were analysed during exposure to the synthetic glucocorticoid, dexamethasone, using noise analysis. These rates were further used to reach specific conclusions about single-channel current, channel density and open probability of the channel in the absence of the blocker. Short-term exposure (3 h) to 10(-7) mol/l dexamethasone at the basolateral side increased the short-circuit current, Isc by 85%, without a change in the ON and OFF rates of the interaction between amiloride and the Na+ channel. A longer incubation (24 h) with dexamethasone tripled the current with a notable increase in the ON rate of the interaction between amiloride and the and channel. The OFF rate remained constant. The effects of dexamethasone on the rate constants of the reaction of amiloride with the channel did not match with the expected changes in membrane potential. On the other hand, ON and OFF rates of the interaction between neutral CDPC and the channel were not influenced by a 24-h incubation with dexamethasone. Further calculations disclosed that the gain in macroscopic current after a 24-h incubation with dexamethasone might be explained by an increase in Na+ channel density, and, to a lesser extent, by a rise in single-channel current. This all occurred without a change in the fraction of time spent by the channel in the conducting state in the absence of the blocker.
使用噪声分析方法，分析了带正电荷的氨氯吡脒或其不带电荷的类似物CDPC（6-氯-3,5-二氨基吡嗪-2-甲酰胺）与肾A6细胞顶端Na⁺通道蛋白的结合（ON）和解离（OFF）速率，实验期间细胞暴露于合成糖皮质激素地塞米松中。这些速率进一步用于得出关于在不存在阻滞剂时单通道电流、通道密度和通道开放概率的具体结论。在基底外侧短期（3小时）暴露于10⁻⁷mol/l地塞米松使短路电流Isc增加了85%，而氨氯吡脒与Na⁺通道相互作用的ON和OFF速率没有变化。用地塞米松孵育更长时间（24小时）使电流增加了两倍，氨氯吡脒与通道相互作用的ON速率显著增加，OFF速率保持不变。地塞米松对氨氯吡脒与通道反应速率常数的影响与预期的膜电位变化不匹配。另一方面，中性CDPC与通道相互作用的ON和OFF速率不受与地塞米松24小时孵育的影响。进一步计算表明，用地塞米松孵育24小时后宏观电流的增加可能是由于Na⁺通道密度增加，以及在较小程度上由于单通道电流增加。所有这些变化发生时，在不存在阻滞剂的情况下通道处于导通状态的时间分数没有改变。
