Aickin C C, Brading A F
J Physiol. 1983 Mar;336:179-97. doi: 10.1113/jphysiol.1983.sp014575.
Cl movements across the cell membranes of smooth muscle from the guinea-pig vas deferens were measured using Cl-sensitive micro-electrodes and 36Cl fluxes. The rate constants for the loss of Cl ions measured by both methods under a variety of conditions were used to calculate the apparent Cl permeability (PCl). If it is assumed that the initial rate of decline of the intracellular Cl activity (aiCl) on removal of extracellular Cl (Clo) represents net transmembrane Cl movement, the apparent PCl was 3-6 X 10(-8) cm s-1. This value is in good agreement with those calculated from the rate constant of 36Cl efflux into both normal Krebs solution (steady-state) and Cl-free solution. Such a value for PCl predicts a large depolarization on removal of Clo, but only a minimal change was recorded. It also predicts that changes in membrane potential (Em) would affect aiCl; furthermore that removal of Clo would increase membrane resistance and thus the hyperpolarization observed on reactivation of the electrogenic Na pump. Neither of these was observed. The PCl/PK ratio obtained from changes in Em on rapid changes in Clo and Ko gives a value for PCl which is an order of magnitude lower: 4 X 10(-9) cm s-1, using Casteels' (1969 b) value for PK. These observations can be reconciled by a substantial proportion of the measured Cl movements being carrier-mediated. The presence of the stilbene derivative DIDS greatly slowed both the steady-state efflux and uptake of 36Cl, as has previously been shown for the loss and reaccumulation of Cl ions on removal and replacement of Clo. PCl calculated in the presence of DIDS was about 5 X 10(-9) cm s-1. The nominal absence of CO2 and HCO3, which slows the reaccumulation and loss of Cl, had no effect on the steady-state fluxes. This indicates that the carrier operates in the self-exchange mode in the steady state.
使用氯离子敏感微电极和³⁶Cl通量测量了豚鼠输精管平滑肌细胞膜上的氯离子移动。在各种条件下，通过两种方法测得的氯离子丢失速率常数用于计算表观氯离子渗透率（PCl）。如果假设去除细胞外氯离子（Clo）后细胞内氯离子活性（aiCl）的初始下降速率代表净跨膜氯离子移动，表观PCl为3 - 6×10⁻⁸ cm s⁻¹。该值与根据³⁶Cl外流速率常数计算得到的值高度一致，该速率常数是在正常 Krebs 溶液（稳态）和无氯溶液中测得的。这样的PCl值预测去除Clo时会发生较大的去极化，但记录到的变化极小。它还预测膜电位（Em）的变化会影响aiCl；此外，去除Clo会增加膜电阻，从而使在电致钠泵重新激活时观察到的超极化现象增强。但这些均未观察到。根据Clo和Ko快速变化时Em的变化获得的PCl/PK比值给出的PCl值低一个数量级：4×10⁻⁹ cm s⁻¹，使用的是Casteels（1969b）的PK值。这些观察结果可以通过相当一部分测得的氯离子移动是由载体介导的来解释。如先前在去除和替换Clo时氯离子的丢失和重新积累所显示的那样，芪衍生物DIDS的存在极大地减慢了³⁶Cl的稳态外流和摄取。在DIDS存在的情况下计算得到的PCl约为5×10⁻⁹ cm s⁻¹。名义上不存在二氧化碳和碳酸氢根离子（这会减慢氯离子的重新积累和丢失）对稳态通量没有影响。这表明载体在稳态下以自交换模式运行。
