Relationship between a HCO3- -permeable conductance and a CLCA protein from rat pancreatic zymogen granules.

Academic Article

Abstract

  • Ca(2+)-induced enzyme secretion in the exocrine pancreas is not completely understood. We have proposed that Ca(2+)-induced enzyme secretion in the exocrine pancreas involves activation of ion conductances in the membrane of zymogen granules (ZG). Here we have identified a Ca(2+)-activated anion conductance in rat pancreatic ZG membranes (ZGM). Ca(2+) (2.5-50 microM) increased the conductance for I(-), NO(3)(-), Br(-), or HCO(3)(-), but not for Cl(-), as determined by the rate of valinomycin-induced osmotic lysis of ZG suspended in isotonic K(+)-salts. 4,4'-Diisothiocyanatodihydrostilbene-2,2'-disulfonate (100 microM) or 25 microM dithiothreitol strongly inhibited Ca(2+)-dependent lysis. The permeability sequence, Ca(2+) dependence, and inhibitor sensitivity of ZG anion conductance are reminiscent of a family of epithelial Ca(2+)-activated anion channels (CLCA). CLCA expression was confirmed by RT-PCR with rat pancreatic mRNA and mouse CLCA1 primers. A PCR product (580bp) 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 the Ca(2+)-activated HCO(3)(-) conductance of rat pancreatic ZGM and contribute to hormone-stimulated enzyme secretion.
  • Keywords

  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid, Amino Acid Sequence, Animals, Bicarbonates, Calcium, Chloride Channels, Dithiothreitol, Electric Conductivity, Exocytosis, Intracellular Membranes, Ion Transport, Male, Molecular Sequence Data, Pancreas, Rats, Rats, Wistar, Reverse Transcriptase Polymerase Chain Reaction, Secretory Vesicles, Sequence Alignment
  • Author List

  • Thévenod F; Roussa E; Benos DJ; Fuller CM
  • Start Page

  • 546
  • End Page

  • 554
  • Volume

  • 300
  • Issue

  • 2