Fröhlich O
J Gen Physiol. 1984 Dec;84(6):877-93. doi: 10.1085/jgp.84.6.877.
The rates of anion net efflux from gramicidin-treated erythrocytes in the presence of a K gradient were measured at 25 degrees C, pH 7.8, as rates of loss of Ki. The experiments served to estimate the relative contributions of two hypothetical mechanisms to Cl net efflux at low extracellular Cl concentrations. Cl, Br, and NO3 net effluxes were measured into media of different Cl, Br, or NO3 concentrations, respectively, to determine and compare the relative rates of the extracellular anion-inhibitable components. They were 48, 160, and 230 mmol/(kg Hb X min), respectively, at a membrane potential of about -90 mV. This indicates that the anion-inhibitable efflux is not due solely to the return translocation of the empty transport site ("slippage") because slippage should be independent of the chemical nature of the anion. Cl net efflux was also measured as a function of the intracellular Cl concentration into media containing either 0 or 50 mM Cl. Under both conditions, net efflux was linearly dependent on Cli between 30 and 300 mM Cli and was 0 when back-extrapolated to 0 Cli. This observation is not compatible with the slippage process, which under these conditions would have been expected to be independent of Cli above 15 mM Cli. It was concluded that slippage contributes negligibly to Cl net efflux even at low extracellular anion concentrations and that the alternative process of "tunneling"--that is, movement of the anion through the anion transporter without a conformational change in a channel-type behavior--is the major, if not the sole, mechanism underlying Cl conductance.
在25摄氏度、pH值为7.8的条件下，测量了在存在钾离子梯度的情况下，短杆菌肽处理的红细胞中阴离子净外流速率，以钾离子损失速率来表示。这些实验旨在估计在低细胞外氯离子浓度下，两种假设机制对氯离子净外流的相对贡献。分别测量了氯离子、溴离子和硝酸根离子向不同氯离子、溴离子或硝酸根离子浓度的介质中的净外流，以确定并比较细胞外阴离子可抑制成分的相对速率。在膜电位约为 -90 mV时，它们分别为48、160和230 mmol/(kg血红蛋白×分钟)。这表明阴离子可抑制的外流并非仅由于空转运位点的反向转运（“滑移”），因为滑移应与阴离子的化学性质无关。还测量了氯离子净外流作为细胞内氯离子浓度的函数，介质中氯离子浓度分别为0或50 mM。在这两种条件下，净外流在30至300 mM细胞内氯离子之间均与细胞内氯离子呈线性相关，当外推至0细胞内氯离子时净外流为0。该观察结果与滑移过程不相符，在这些条件下，预计滑移在细胞内氯离子高于15 mM时应与细胞内氯离子无关。得出的结论是，即使在低细胞外阴离子浓度下，滑移对氯离子净外流的贡献也可忽略不计，并且“隧道效应”这一替代过程——即阴离子通过阴离子转运体移动而通道型行为无构象变化——是氯离子传导的主要机制，即便不是唯一机制。
