Marshall W S, Bryson S E
Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia, Canada.
Am J Physiol. 1991 Sep;261(3 Pt 2):R652-8. doi: 10.1152/ajpregu.1991.261.3.R652.
We measured intracellular pH (pHi) of single epithelial cells in situ in the urinary bladder epithelium using microspectrofluorometry and the cytoplasmically trapped pH-sensitive fluorophore, 2',7'-bis(2-carboxyethyl)-5(6)- carboxyfluorescein (BCECF). The resting pHi was 7.21 +/- 0.03 (n = 40 bladders, 489 cells) in pH 7.8 bathing solutions, indicating that H+ is not passively distributed across the plasma membrane and is extruded against its electrochemical gradient. Whereas exposure to hypercapnia (5% CO2 saturation) reversibly decreased pHi, mucosally added 20 mM NH4+ reversibly increased pHi. Recovery from the NH4+ effect was slow and lacked an acid-load pHi undershoot; this is interpreted as suggesting significant NH4+ permeability. Recovery from hypercapnic acidosis was blocked by mucosally added amiloride, indicating that apical Na(+)-H+ exchange is involved in pHi regulation. Addition of 0.5 mM NH4+ to the basolateral side when the mucosal side was bathed in mock urine (2 mM NaCl) significantly increased undirectional mucosal-to-serosal Na+ flux, and the increase was blocked by mucosally added amiloride. We conclude that an apically located Na(+)-H+ exchange is important in pHi regulation and may also accept NH4+ as the counterion for Na+.
我们使用显微分光荧光测定法和胞质截留的pH敏感荧光团2',7'-双（2-羧乙基）-5（6）-羧基荧光素（BCECF），原位测量膀胱上皮单个上皮细胞的细胞内pH（pHi）。在pH 7.8的浴液中，静息pHi为7.21±0.03（n = 40个膀胱，489个细胞），这表明H+并非被动地分布于质膜两侧，而是逆着其电化学梯度被排出。暴露于高碳酸血症（5% CO2饱和度）会使pHi可逆性降低，而黏膜添加20 mM NH4+会使pHi可逆性升高。从NH4+作用中恢复缓慢且缺乏酸负荷pHi下冲；这被解释为提示存在显著的NH4+通透性。黏膜添加氨氯吡咪可阻断从高碳酸血症性酸中毒中的恢复，表明顶端Na(+)-H+交换参与pHi调节。当黏膜侧用模拟尿液（2 mM NaCl）灌注时，向基底外侧添加0.5 mM NH4+可显著增加单向的黏膜到浆膜的Na+通量，且该增加被黏膜添加的氨氯吡咪所阻断。我们得出结论，位于顶端的Na(+)-H+交换在pHi调节中很重要，并且也可能接受NH4+作为Na+的抗衡离子。
