HCO3- secretion by murine nasal submucosal gland serous acinar cells during Ca2+-stimulated fluid secretion
HCO3- secretion by murine nasal submucosal gland serous acinar cells during Ca2+-stimulated fluid secretion
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DOI：
10.1085/jgp.200810017
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发表时间：
2008-07-01
影响因子：
3.8
通讯作者：
Foskett, J. Kevin
中科院分区：
文献类型：
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作者：
Lee, Robert J.;Harlow, Janice M.;Foskett, J. Kevin
呼吸道粘膜下腺构成了呼吸道表面液体(ASL)的组成和体积，对肺粘膜纤毛清除都很重要。浆液性腺泡产生了腺体分泌的大部分液体，但其分子机制尚不清楚。我们先前在同步差示干涉对比(DIC)和荧光显微镜下描述了在原代小鼠浆液腺泡细胞中，由钙激活的氯-分泌驱动的胆碱能调节液体分泌。在这里，我们通过同时测量细胞内pH(pH(I))和细胞体积来评估钙激活的Cl-分泌是否伴随着HCO3-的分泌，HCO3-可能是ASL的一个关键成分。在生理介质(5%CO2-25 mMHCO3-)中，静息pH(I)为7.17+/-0.01。在卡巴胆碱(CCH)刺激过程中，pH(I)瞬间下降0.08+/-0.01U，同时细胞收缩显示氯含量下降，反映了氯-的分泌。随后的碱化使pH(I)上升到静息水平以上，直到激动剂被移除，然后恢复到刺激前的值。在名义上无CO2-HCO3的介质中，CCH诱导的酸化减少，而碱化保持不变。离子替代或氯离子通道阻滞剂尼氟米酸(100 MM)可消除传导HCO3-外流驱动力，分别强烈抑制激动剂诱导的酸化作用。Na+/H+交换(NHE)阻滞剂二甲基米洛利(DMA)可使CCH诱导的酸化程度增加一倍以上，持续时间延长一倍以上。基因表达谱显示浆液细胞表达NHE亚型1-4和6-9，但药理学敏感性表明，在CCH刺激和激动剂诱导的酸化后pH(I)恢复过程中观察到的碱化主要是由于NHE1，定位于基底膜。这些结果表明，浆液性腺泡细胞在钙离子刺激的液体分泌过程中通过参与顶膜分泌氯通道的机制分泌HCO3-，而HCO3-的分泌是通过激活基底膜上的NHE1来维持的。此外，还存在其他依赖于Na+的pH(I)调节机制，如在无Na+的介质中对碱化的较强抑制。
Airway submucosal glands contribute to airway surface liquid (ASL) composition and volume, both important for lung mucociliary clearance. Serous acini generate most of the fluid secreted by glands, but the molecular mechanisms remain poorly characterized. We previously described cholinergic-regulated fluid secretion driven by Ca2+-activated Cl- secretion in primary murine serous acinar cells revealed by simultaneous differential interference contrast (DIC) and fluorescence microscopy. Here, we evaluated whether Ca2+-activated Cl- secretion was accompanied by secretion of HCO3-, possibly a critical ASL component, by simultaneous measurements of intracellular pH (pH(i)) and cell volume. Resting pH(i) was 7.17 +/- 0.01 in physiological medium (5% CO2-25 mM HCO3-). During carbachol (CCh) stimulation, pH(i) fell transiently by 0.08 +/- 0.01 U concomitantly with a fall in Cl- content revealed by cell shrinkage, reflecting Cl- secretion. A subsequent alkalinization elevated pH(i) to above resting levels until agonist removal, whereupon it returned to prestimulation values. In nominally CO2-HCO3- -free media, the CCh-induced acidification was reduced, whereas the alkalinization remained intact. Elimination of driving forces for conductive HCO3- efflux by ion substitution or exposure to the Cl- channel inhibitor niflumic acid (100 mu M) strongly inhibited agonist-induced acidifi cation by > 80% and > 70%, respectively. The Na+/H+ exchanger (NHE) inhibitor dimethylamiloride (DMA) increased the magnitude (greater than twofold) and duration of the CCh-induced acidifi cation. Gene expression profiling suggested that serous cells express NHE isoforms 1-4 and 6-9, but pharmacological sensitivities demonstrated that alkalinization observed during both CCh stimulation and pH(i) recovery from agonist-induced acidification was primarily due to NHE1, localized to the basolateral membrane. These results suggest that serous acinar cells secrete HCO3- during Ca2+-evoked fluid secretion by a mechanism that involves the apical membrane secretory Cl- channel, with HCO3- secretion sustained by activation of NHE1 in the basolateral membrane. In addition, other Na+-dependent pH(i) regulatory mechanisms exist, as evidenced by stronger inhibition of alkalinization in Na+-free media.