A New Role for Bicarbonate in Mucus Formation.

06:00 EDT 10th August 2010 | BioPortfolio

Summary of "A New Role for Bicarbonate in Mucus Formation."

The impact of small anions on the physical properties of gel-forming mucin has been almost overlooked relative to that of cations. Recently, based on the coincident abnormalities in HCO(3)(-) secretion and abnormal mucus formed in the hereditary disease, Cystic Fibrosis (CF), HCO(3)(-) was hypothesized to be critical in the formation of normal mucus by virtue of its ability to sequester Ca(2+) from condensed mucins being discharged from cells. However, direct evidence of the impact of HCO(3)(-) on mucus properties is lacking. Herein, we demonstrate for the first time that mucin diffusivity (~1/viscosity) increases as a function of [HCO(3)(-)]. Direct measurements of exocytosed mucin swelling kinetics from airway cells showed that mucin diffusivity increases by ~300 percent with 20 mM extracellular HCO(3)(-) concentration. Supporting data indicate that HCO(3)(-) reduces free Ca(2+) concentration and decreases the amount of Ca(2+) that remains associated with mucins. The results demonstrate that HCO(3)(-) enhances mucin swelling and hydration by reducing Ca(2+) cross-linking in mucins, thereby decreasing its viscosity and likely increasing its transportability. In addition, HCO(3)(-) can function as a Ca(2+) chelator like EGTA (ethylene glycol tetraacetic acid) to disperse mucin aggregates. This study indicates that poor HCO(3)(-) availability in CF may explain why secreted mucus remains aggregated and more viscous in affected organs. These insights bear not only the fundamental pathogenesis in CF, but also on the process of gel mucus formation and release in general.


1University of California Merced.

Journal Details

This article was published in the following journal.

Name: American journal of physiology. Lung cellular and molecular physiology
ISSN: 1522-1504


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