Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6085, USA.
J Clin Invest. 2010 Sep;120(9):3137-48. doi: 10.1172/JCI42992. Epub 2010 Aug 25.
Cystic fibrosis (CF), which is caused by mutations in CFTR, affects many tissues, including the lung. Submucosal gland serous acinar cells are primary sites of fluid secretion and CFTR expression in the lung. Absence of CFTR in these cells may contribute to CF lung pathogenesis by disrupting fluid secretion. Here, we have isolated primary serous acinar cells from wild-type and CFTR-/- pigs and humans without CF to investigate the cellular mechanisms and regulation of fluid secretion by optical imaging. Porcine and human serous cells secrete fluid in response to vasoactive intestinal polypeptide (VIP) and other agents that raise intracellular cAMP levels; here, we have demonstrated that this requires CFTR and a cAMP-dependent rise in intracellular Ca2+ concentration ([Ca2+]i). Importantly, cAMP induced the release of Ca2+ from InsP3-sensitive Ca2+ stores also responsive to cAMP-independent agonists such as cholinergic, histaminergic, and purinergic agonists that stimulate CFTR-independent fluid secretion. This provides two types of synergism that strongly potentiated cAMP-mediated fluid secretion but differed in their CFTR dependencies. First, CFTR-dependent secretion was strongly potentiated by low VIP and carbachol concentrations that individually were unable to stimulate secretion. Second, higher VIP concentrations more strongly potentiated the [Ca2+]i responses, enabling ineffectual levels of cholinergic stimulation to strongly activate CFTR-independent fluid secretion. These results identify important molecular mechanisms of cAMP-dependent secretion, including a requirement for Ca2+ signaling, and suggest new therapeutic approaches to correct defective submucosal gland secretion in CF.
囊性纤维化（CF）是由 CFTR 突变引起的，它影响许多组织，包括肺部。黏膜下腺浆液性腺泡细胞是肺部液体分泌和 CFTR 表达的主要部位。这些细胞中 CFTR 的缺失可能通过破坏液体分泌而导致 CF 肺部发病机制。在这里，我们从野生型和 CFTR-/-猪和非 CF 人类中分离出了原发性浆液腺泡细胞，以通过光学成像研究液体分泌的细胞机制和调节。猪和人浆液细胞对血管活性肠肽（VIP）和其他能提高细胞内环腺苷酸（cAMP）水平的物质作出反应而分泌液体；在这里，我们已经证明这需要 CFTR 和 cAMP 依赖性的细胞内 Ca2+浓度升高([Ca2+]i)。重要的是，cAMP 诱导了 InsP3 敏感 Ca2+库中 Ca2+的释放，该库也对 cAMP 非依赖性激动剂（如胆碱能、组胺能和嘌呤能激动剂）有反应，这些激动剂刺激 CFTR 非依赖性液体分泌。这提供了两种类型的协同作用，强烈增强了 cAMP 介导的液体分泌，但在 CFTR 依赖性方面存在差异。首先，CFTR 依赖性分泌强烈受到低 VIP 和卡巴胆碱浓度的增强，而单独这些浓度不能刺激分泌。其次，较高的 VIP 浓度更强烈地增强了[Ca2+]i 反应，使无效水平的胆碱能刺激能强烈激活 CFTR 非依赖性液体分泌。这些结果确定了 cAMP 依赖性分泌的重要分子机制，包括对 Ca2+信号的要求，并提出了纠正 CF 中黏膜下腺分泌缺陷的新治疗方法。
