151. Relationship between a <f>HCO3−</f>-permeable conductance and a CLCA protein from rat pancreatic zymogen granules
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Thévenod, Frank, Roussa, Eleni, Benos, Dale J., and Fuller, Catherine M.
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EXOCYTOSIS , *IMMUNOBLOTTING - Abstract
Ca2+ -induced enzyme secretion in the exocrine pancreas is not completely understood. We have proposed thatCa2+ -induced enzyme secretion in the exocrine pancreas involves activation of ion conductances in the membrane of zymogen granules (ZG). Here we have identified aCa2+ -activated anion conductance in rat pancreatic ZG membranes (ZGM).Ca2+ (2.5–50μ M) increased the conductance forI− ,NO3− ,Br− , orHCO3− , but not forCl− , as determined by the rate of valinomycin-induced osmotic lysis of ZG suspended in isotonicK+ -salts. 4,4′ -Diisothiocyanatodihydrostilbene-2,2′ -disulfonate (100μ M) or 25μ M dithiothreitol strongly inhibitedCa2+ -dependent lysis. The permeability sequence,Ca2+ dependence, and inhibitor sensitivity of ZG anion conductance are reminiscent of a family of epithelialCa2+ -activated anion channels (CLCA). CLCA expression was confirmed by RT-PCR with rat pancreatic mRNA and mouse CLCA1 primers. A PCR product (580 bp) exhibited 81%, 77%, and 57% amino acid similarity to the three mouse isoforms mCLCA-1, -2, and -3 (mgob-5), respectively. Antibodies against bovine tracheal CLCA1 showed CLCA expression in ZGM by immunoblotting, immunoperoxidase light microscopy, and immunogold labeling. These findings suggest that a CLCA-related protein could account for theCa2+ -activatedHCO3− conductance of rat pancreatic ZGM and contribute to hormone-stimulated enzyme secretion. [Copyright &y& Elsevier]- Published
- 2003
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