Tissue and Cell Distribution of Parchorin, a Chloride Intracellular Channel-Related Protein

Abstract

We previously reported a 120 kDa phosphoprotein that translocated from cytosol to the apical membrane of gastric parietal cells in association with stimulation of HCl secretion (8). Recently, we cloned this protein from rabbit choroid plexus and named it “parchorin” based on its high enrichment in parietal cells and choroid plexus (6). Parchorin is a novel protein with 64 kDa that has significant homology to the family of chloride intracellular channels (CLIC), especially the chloride channel from bovine kidney, p64, in its C-terminal 235 amino acids (Fig. 1). In contrast to other CLIC family members, most of which are considered to be Cl- channels in intracellular vesicles (7), parchorin is a soluble cytosolic phosphoprotein which translocates to the plasma membrane under stimulation. When acid-secreting parietal cell is stimulated, tubulovesicles containing H,K-ATPase fuse with the apical membrane, and both K+ and Cl- permeability in the apical membrane is increased. During this activation process, it was observed that parchorin translocated from cytosol to the apical membrane (6, 8). It was also observed that parchorin, transfected to LLC-PK1 cell, translocated to the plasma membrane and accelerated the Cl- efflux rate when Cl- efflux was caused by elimination of [Cl]o (6). Using Northern and Western blotting, it has been found that parchorin preferentially distributes to tissues related to water movement, i.e., gastric mucosa, choroid plexus, salivary gland, and kidney (6, 8). Parchorin was named by its characteristic distribution, i.e., the highest expression in parietal cell and choroid plexus. These observations strongly suggest that parchorin plays an important role in the regulated movement of body fluid via Cl- transport.