Canessa M, Labarca P, DiBona D R, Leaf A
Proc Natl Acad Sci U S A. 1978 Sep;75(9):4591-5. doi: 10.1073/pnas.75.9.4591.
The ratio of the rate of transepithelial sodium transport, JNa, across the isolated toad urinary bladder to the simultaneously measured rate of transport-dependent metabolism, JsbCO2, has been measured as a function of the transepithelial electrical voltage, deltapsi. The ratio remains constant with a mean value of 18 to 20 over the range of imposed voltages of 0 to +70 mV. With increasing hyperpolarization of the bladder, JNa decreases and the calculated electromotive force or apparent "ENa" of the sodium pump increases. From thermodynamic and kinetic arguments it is shown that the apparent "ENa" approaches the maximal electrochemical potential gradient, ENa, against which sodium can be transported by this tissue only when JNa approximately 0. At this unique condition F ENa (in which F is the Faraday constant) is the maximal free energy of the chemical reaction driving sodium transport and thus equal to the maximal extramitochondrial phosphorylation potential and the maximal free energy of the mitochondrial respiratory chain within the transporting cells.
已测量了经分离的蟾蜍膀胱的跨上皮钠转运速率JNa与同时测量的转运依赖性代谢速率JsbCO2的比值，该比值是跨上皮电压deltapsi的函数。在0至+70 mV的外加电压范围内，该比值保持恒定，平均值为18至20。随着膀胱超极化程度的增加，JNa降低，钠泵的计算电动势或表观“ENa”增加。从热力学和动力学角度论证表明，仅当JNa约为0时，表观“ENa”才接近最大电化学势梯度ENa，在此条件下该组织能够逆着该梯度转运钠。在这一独特条件下，F ENa（其中F为法拉第常数）是驱动钠转运的化学反应的最大自由能，因此等于转运细胞内最大的线粒体外磷酸化电位以及线粒体呼吸链的最大自由能。
