Krouse Mauri E, Talbott Jason F, Lee Martin M, Joo Nam Soo, Wine Jeffrey J
Cystic Fibrosis Research Laboratory, Stanford University, Stanford, CA 94305, USA.
Am J Physiol Lung Cell Mol Physiol. 2004 Dec;287(6):L1274-83. doi: 10.1152/ajplung.00036.2004. Epub 2004 Aug 13.
Submucosal glands are the primary source of airway mucus, a critical component of lung innate defenses. Airway glands are defective in cystic fibrosis (CF), showing a complete absence of secretion to vasoactive intestinal peptide or forskolin, which increase intracellular cAMP concentration. This defect is attributed to gland serous cells, which express the cystic fibrosis transmembrane conductance regulator. Calu-3 cells, which mimic many features of serous cells, secrete Cl(-) and HCO(3)(-), with HCO(3)(-) secretion predominating for forskolin stimulation and Cl(-) secretion predominating for stimuli that open basolateral K(+) channels to hyperpolarize the cells. We used pH stat and ion substitution experiments to clarify the mechanisms and consequences of these two modes of secretion. We confirm that Calu-3 cells secrete primarily HCO(3)(-) in response to forskolin. Unexpectedly, HCO(3)(-) secretion continued in response to K(+) channel openers, with Cl(-) secretion being added to it. Secretion of HCO(3)(-) from hyperpolarized cells occurs via the conversion of CO(2) to HCO(3)(-) and is reduced by approximately 50% with acetazolamide. A gap between the base equivalent current and short-circuit current was observed in all experiments and was traced to secretion of H(+) via a ouabain-sensitive, K(+)-dependent process (possibly H(+)-K(+)-ATPase), which partially neutralized the secreted HCO(3)(-). The conjoint secretion of HCO(3)(-) and H(+) may help explain the puzzling finding that mucus secreted from normal and CF glands has the same acidic pH as does mucus from glands stimulated with forskolin or ACh. It may also help explain how human airway glands produce mucus that is hypotonic.
黏膜下腺是气道黏液的主要来源，而气道黏液是肺部固有防御的关键组成部分。囊性纤维化（CF）患者的气道腺存在缺陷，对血管活性肠肽或福斯可林（可增加细胞内cAMP浓度）完全无分泌反应。这种缺陷归因于腺浆液细胞，其表达囊性纤维化跨膜传导调节因子。Calu-3细胞模拟了浆液细胞的许多特征，分泌Cl(-)和HCO(3)(-)，福斯可林刺激时以HCO(3)(-)分泌为主，而打开基底外侧K(+)通道使细胞超极化的刺激则以Cl(-)分泌为主。我们使用pH稳态和离子替代实验来阐明这两种分泌模式的机制和后果。我们证实，Calu-3细胞对福斯可林的反应主要分泌HCO(3)(-)。出乎意料的是，K(+)通道开放剂刺激时HCO(3)(-)分泌持续，同时还伴有Cl(-)分泌增加。超极化细胞分泌HCO(3)(-)是通过将CO(2)转化为HCO(3)(-)实现的，乙酰唑胺可使其减少约50%。在所有实验中均观察到碱基等效电流和短路电流之间存在差距，这可追溯到通过哇巴因敏感、K(+)依赖过程（可能是H(+)-K(+)-ATP酶）分泌H(+)，该过程部分中和了分泌的HCO(3)(-)。HCO(3)(-)和H(+)的联合分泌可能有助于解释一个令人困惑的发现，即正常和CF腺体分泌的黏液与用福斯可林或乙酰胆碱刺激的腺体分泌的黏液具有相同的酸性pH值。这也可能有助于解释人类气道腺如何产生低渗黏液。
