Nagel W, Shalitin Y, Katz U
Department of Physiology, University of Munich, Germany.
Cell Physiol Biochem. 1998;8(4):212-23. doi: 10.1159/000016284.
The effect of aminoperimidine (AP) on transepithelial Na+ transport and Cl- conductance (G(Cl)) of isolated amphibian skin (Bufo viridis and Rana esculenta) was analyzed using transepithelial and intracellular electrophysiological techniques. AP, applied at concentrations between 30 and 100 microM from the mucosal side, stimulated Na+ transport rapidly and reversibly by more than 30% of the control value due to an increase in apical membrane Na+ permeability. Influence of AP on basolateral membrane conductance and effective driving force for Na+ were negligible. Voltage-activated G(Cl) of toad skin, but not the resting, deactivated conductance, as well as spontaneously high G(Cl) in frog skin was rapidly inhibited by AP in a concentration-dependent manner. The half-maximal inhibitory concentration of 20 microM is the highest hitherto reported inhibitory power for G(Cl) in amphibian skin. The effect of AP on G(Cl) was slowly and incompletely reversible even after brief exposure to the agent. Serosal application of AP had similar, albeit delayed effects on both Na+ and Cl- transport. AP did not interfere with the Cl- pathway after it was opened by 100-300 microM CPT-cAMP, a membrane-permeable, nonhydrolyzed analogue of cAMP. Inhibition of the voltage-activated G(Cl) by AP was attenuated or missing when AP was applied during voltage perturbation to serosa-positive potentials. Since AP is positively charged at physiological pH, it suggests that the affected site is located inside the Cl- pathway at a certain distance from the external surface. AP affects then the Na+ and Cl- transport pathways independent of each other. The nature of chemical interference with AP, which is responsible for the influence on the transport of Na+ and Cl-, remains to be elucidated.
运用跨上皮和细胞内电生理技术，分析了氨基嘧啶（AP）对离体两栖类皮肤（绿蟾蜍和食用蛙）跨上皮Na⁺转运及Cl⁻电导（G(Cl)）的影响。从黏膜侧施加浓度为30至100微摩尔的AP，由于顶端膜Na⁺通透性增加，可迅速且可逆地刺激Na⁺转运，使其比对照值增加30%以上。AP对基底外侧膜电导及Na⁺有效驱动力的影响可忽略不计。蟾蜍皮肤的电压激活型G(Cl)，而非静息、失活电导，以及蛙皮肤中自发的高G(Cl)，会被AP以浓度依赖的方式迅速抑制。20微摩尔的半数最大抑制浓度是迄今报道的对两栖类皮肤G(Cl)的最高抑制能力。即使短暂接触该试剂后，AP对G(Cl)的影响也是缓慢且不完全可逆的。从浆膜侧施加AP对Na⁺和Cl⁻转运有类似影响，不过作用延迟。在100 - 300微摩尔的环磷腺苷（cAMP）膜通透性非水解类似物CPT - cAMP打开Cl⁻通道后，AP不会干扰Cl⁻途径。当在浆膜侧施加正电位的电压扰动期间应用AP时，AP对电压激活型G(Cl)的抑制作用减弱或消失。由于AP在生理pH下带正电荷，这表明受影响的位点位于Cl⁻途径内部距外表面一定距离处。AP对Na⁺和Cl⁻转运途径的影响相互独立。导致对Na⁺和Cl⁻转运产生影响的AP化学干扰性质仍有待阐明。
