Cl--ATPase in rat brain and kidney

Cl--stimulated ATPase/ATP-dependent CT pump (Cl--ATPase/pump) has been foun d as a candidate for an active outwardly directed Cl- transporter in brain neurons. (1) A 520-kDa protein complex with Cl--ATPase/pump activity was is olated from rat brain. It consisted of four protein subunits (51, 55, 60, a nd 62 kDa proteins), the 51-kDa protein being a covalent phosphorylenzyme s ubunit. (2) An antiserum against the 51-kDa protein inhibited Cl--ATPase/pu mp activity. Western blot analysis showed an immunoreactive 51-kDa protein in the brain, spinal cord, and kidney. By enzyme histochemistry and immunoh istochemistry, Cl--ATPase-like activity or immunoreactivity was observed on the plasma membranes of brain neurons, and on the base-lateral membranes o f type A intercalated cells of renal collecting ducts. (3) Reconstituted Cl --ATPase/pump activity was highest in liposomes with phosphatidylinositol-4 -monophosphate. LiCl, an inhibitor of inositolphosphatase, reduced Cl--ATPa se activity and increased intracellular Cl- concentrations in cultured rat hippocampal neurons with increased phosphatidylinositol turnover. (4) In th e brains of patients with Alzheimer's disease (AD), where phosphatidylinosi tol 4-kinase activity is reduced, Cl--ATPase activity was also reduced. Thu s, Cl--ATPase is likely an outwardly directed ATP-dependent Cl- transporter that consists of four subunits and is regulated by phosphatidylinositol-4- monophosphate. Changes in Cl--ATPase activity may be related to the pathoph ysiology of human neurodegenerative diseases. (C) 2001 Wiley-Liss, Inc.