Calcium binding to biliary mucins is dependent on sodium ion concentration: relevance to cystic fibrosis |
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Authors: | Kuver Rahul Lee Sum P |
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Institution: | Division of Gastroenterology, University of Washington School of Medicine, Seattle, WA 98195, USA. kuver@u.washington.edu |
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Abstract: | Because hypersecretion of gallbladder (GB) mucus occurs in gallstone formation and because binding of Ca(2+) to biliary lipids only accounts for 50% of the total Ca(2+) in GB bile, we investigated the binding of Ca(2+) to human biliary mucin. Biliary mucin was purified from GB bile and binding to Ca(2+) studied. Scatchard plot analysis suggested two binding sites. Removal of sialic acid by neuraminidase resulted in 10% reduction of Ca(2+) binding, whereas, sulfatase treatment reduced Ca(2+) binding by 30%. Using a hypotonic NaCl solution, Ca(2+) binding to mucin increased curvilinearly with mucin concentration. However, binding decreased with increasing ionic strength of the NaCl solution. We conclude that binding of Ca(2+) to mucin is effected mainly through sulfate. Binding to Ca(2+) can be displaced by Na(+). Ca(2+) binding to mucins is enhanced in the setting of low Na(+) concentrations. This phenomenon has pathophysiologic implications for the formation of thick mucus in cystic fibrosis epithelia. |
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Keywords: | Bile Bile ducts Cystic fibrosis transmembrane conductance regulator Gallbladder Gallstones Mucus |
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