Duffey M E
Am J Physiol. 1984 May;246(5 Pt 1):C558-61. doi: 10.1152/ajpcell.1984.246.5.C558.
The short-circuited epithelium of rabbit colon is thought to actively absorb chloride ion by a mechanism in the mucosal cell membrane that exchanges chloride for bicarbonate ion. If this model is correct bicarbonate may be accumulated above electrochemical equilibrium across the mucosal cell membrane. To test this model intracellular pH was measured using a new hydrogen ion-selective liquid membrane microelectrode that is fast, highly selective, and easy to fabricate with a very small tip diameter. These measurements show that the average intracellular pH in this epithelium is 6.9 +/- 0.1. The mucosal cell membrane electrical potential difference, measured by conventional open-tipped microelectrodes, averaged -52 +/- 3 mV. Intracellular pH is above a value predicted for an equilibrium distribution of hydrogen ion across both cell membranes, implying that a mechanism exists for "uphill" extrusion of this ion from the cell. Intracellular bicarbonate activity calculated from these measurements averaged 8 +/- 1 mM. The electrochemical potential gradient for bicarbonate across the mucosal membrane averaged -28 +/- 2 mV, demonstrating that intracellular bicarbonate is concentrated above an equilibrium distribution across the mucosal membrane. Thus energy in the "downhill" electrochemical potential gradient for bicarbonate exit from the cell may drive the entrance of chloride into this epithelium and energize transepithelial chloride absorption.
兔结肠短路上皮细胞被认为通过黏膜细胞膜上一种用氯离子交换碳酸氢根离子的机制来主动吸收氯离子。如果这个模型是正确的，那么碳酸氢根可能会在黏膜细胞膜上积累到超过电化学平衡的水平。为了验证这个模型，使用一种新型氢离子选择性液膜微电极测量细胞内pH值，该微电极响应速度快、选择性高且易于制作，尖端直径非常小。这些测量结果表明，该上皮细胞的平均细胞内pH值为6.9±0.1。用传统开口尖端微电极测量的黏膜细胞膜电位差平均为-52±3 mV。细胞内pH值高于根据氢离子在两个细胞膜间平衡分布预测的值，这意味着存在一种将该离子从细胞中“上坡”挤出的机制。根据这些测量结果计算出的细胞内碳酸氢根活性平均为8±1 mM。碳酸氢根跨黏膜膜的电化学势梯度平均为-28±2 mV，表明细胞内碳酸氢根在跨黏膜膜的平衡分布之上被浓缩。因此，碳酸氢根从细胞中“下坡”电化学势梯度中的能量可能驱动氯离子进入该上皮细胞，并为跨上皮氯离子吸收提供能量。
