Van Driessche W, Desmedt L, Simaels J
Laboratory for Physiology, KU Leuven, Belgium.
Pflugers Arch. 1991 Apr;418(3):193-203. doi: 10.1007/BF00370514.
The blockage of Na+ movements through the poorly selective cation channels in the apical membrane of frog skin (Rana temporaria) and toad urinary bladder (Bufo marinus) was investigated with noise, impedance analysis and microelectrode techniques. Na+ currents through this pathway were studied with NaCl Ringer solutions on both sides. After removal of Ca2+ and other divalent cations from the mucosal compartment, a considerable part of Isc became insensitive to amiloride. In frog skin, the inhibitory effect of amiloride in mucosal Ca(2+)-free solutions was highly variable. In some experiments a complete lack of inhibition was observed. Similarly, in the absence of amiloride, the inhibitory effect of mucosal Ca2+ varied strongly among frogs. In the absence of mucosal Ca2+, analysis of the fluctuation in Isc revealed a Lorentzian component in the power density spectrum. The corner frequency (fc) of this spontaneous Lorentzian was 12.3 Hz in frog skin and 347 Hz in the toad urinary bladder. In frog skin, nanomolar concentrations of mucosal Ca2+ induced an additional Lorentzian noise component. Its corner frequency shifted upwards with increasing mucosal Ca2+ concentration ([Ca2+]m). The relation between 2 pi fc and [Ca2+]m was linear at small [Ca2+]m whereas a parabolic increase of fc was observed at the highest [Ca2+]m. In the bladder, nanomolar concentrations of mucosal Ca2+ did not induce an additional noise component but modified the spontaneous Lorentzian noise by increasing fc proportionally with [Ca2+]m. Microelectrode recordings demonstrated that at least part of the Ca(2+)-blockable current passes through the granulosum cells and confirmed the apical localization of the poorly selective cation channel. The lack of the inhibitory effect of amiloride in Ca(2+)-free solutions seems to originate from the parallel arrangement of the amiloride- and Ca(2+)-blockable pathways and from influences of the blockage of apical channels on the basolateral membrane conductances. The latter cross-talk seems to find its origin in the voltage dependence of the basolateral membrane conductance [Garty H (1984) J Membr Biol 77:213-222; Nagel W (1985) Pflügers Arch 405 [Suppl 1]:S39-S43].
运用噪声、阻抗分析和微电极技术，研究了蛙皮（林蛙）和蟾蜍膀胱（海蟾蜍）顶端膜中选择性较差的阳离子通道对Na⁺移动的阻断作用。通过该途径的Na⁺电流用两侧均为NaCl林格液进行研究。从黏膜腔室中去除Ca²⁺和其他二价阳离子后，相当一部分短路电流（Isc）对氨氯吡脒不敏感。在蛙皮中，黏膜无Ca²⁺溶液中氨氯吡脒的抑制作用变化很大。在一些实验中，观察到完全没有抑制作用。同样，在没有氨氯吡脒的情况下，黏膜Ca²⁺的抑制作用在不同蛙之间差异也很大。在没有黏膜Ca²⁺的情况下，对Isc波动的分析揭示了功率密度谱中的洛伦兹分量。蛙皮中这种自发洛伦兹分量的转折频率（fc）为12.3Hz，蟾蜍膀胱中为347Hz。在蛙皮中，纳摩尔浓度的黏膜Ca²⁺会诱导出一个额外的洛伦兹噪声分量。其转折频率随黏膜Ca²⁺浓度（[Ca²⁺]m）的增加而向上移动。在低[Ca²⁺]m时，2πfc与[Ca²⁺]m之间的关系是线性的，而在最高[Ca²⁺]m时，观察到fc呈抛物线增加。在膀胱中，纳摩尔浓度的黏膜Ca²⁺不会诱导出额外的噪声分量，但会通过与[Ca²⁺]m成比例增加fc来改变自发的洛伦兹噪声。微电极记录表明，至少部分可被Ca²⁺阻断的电流通过颗粒层细胞，并证实了选择性较差的阳离子通道的顶端定位。在无Ca²⁺溶液中氨氯吡脒缺乏抑制作用似乎源于氨氯吡脒和可被Ca²⁺阻断的途径的平行排列，以及顶端通道阻断对基底外侧膜电导的影响。后者的串扰似乎源于基底外侧膜电导的电压依赖性[加蒂H（1984年）《膜生物学杂志》77:213 - 222；纳格尔W（1985年）《普弗吕格尔氏 Archiv》第405卷[增刊1]:S39 - S43]。
