Aitken M L, Verdugo P
Dept. of Internal Medicine, University of Washington, Seattle 98195.
Symp Soc Exp Biol. 1989;43:73-80.
Mucin, the principal polymeric species in the mucus matrix, is condensed inside secretory granules and undergoes massive swelling upon exocytosis. Mucin swelling is governed by a Donnan equilibrium. However, the effect of polyions such as soluble proteins on the swelling of mucin granules has not been investigated. The experiments reported here were designed to evaluate the effect of albumin on swelling kinetics of mucin granules exocytosed from respiratory goblet cells in culture. The kinetics of swelling was monitored by video-microscopy. The diffusivity of newly released mucins, in the presence of different concentrations of serum albumin, was evaluated using the expression: D = r2f/tau where tau is the characteristic time of the swelling, and rf is the final equilibrium radius of the swollen granule. Preliminary results indicate that serum albumin at concentrations of 10(-7) M, which are equivalent to those found in the bronchial mucus of asthmatic or cystic fibrosis patients, can produce up to a 90% decrease in the diffusivity of newly released mucins. Albumin is commonly present on the surface of the respiratory mucosa, and its concentration is increased in asthma and other bronchial inflammatory diseases. The evidence presented here shows that soluble proteins can strongly modulate the rate of swelling of newly released mucins, as predicted by Donnan equilibrium. Since swelling is a critical determinant of mucus rheology, the concentration of plasma proteins on the mucosa could play an important role in the regulation of the rheological properties of mucus. Also, the characteristically thick mucus found in chronic bronchial inflammatory diseases could be at least partially explained by the high levels of albumin found in the airways of these patients.
黏蛋白是黏液基质中的主要聚合物种类，在分泌颗粒内浓缩，胞吐时会发生大量肿胀。黏蛋白的肿胀受唐南平衡控制。然而，诸如可溶性蛋白质等聚离子对黏蛋白颗粒肿胀的影响尚未得到研究。本文报道的实验旨在评估白蛋白对培养的呼吸道杯状细胞胞吐的黏蛋白颗粒肿胀动力学的影响。通过视频显微镜监测肿胀动力学。在不同浓度血清白蛋白存在的情况下，使用表达式D = r2f/tau评估新释放黏蛋白的扩散系数，其中tau是肿胀的特征时间，rf是肿胀颗粒的最终平衡半径。初步结果表明，浓度为10(-7) M的血清白蛋白（相当于哮喘或囊性纤维化患者支气管黏液中的浓度）可使新释放黏蛋白的扩散系数降低多达90%。白蛋白通常存在于呼吸道黏膜表面，在哮喘和其他支气管炎症性疾病中其浓度会升高。此处提供的证据表明，如唐南平衡所预测的，可溶性蛋白质可强烈调节新释放黏蛋白的肿胀速率。由于肿胀是黏液流变学的关键决定因素，黏膜上血浆蛋白的浓度可能在黏液流变学特性的调节中起重要作用。此外，慢性支气管炎症性疾病中典型的浓稠黏液至少部分可以由这些患者气道中高水平的白蛋白来解释。
