LOCALIZATION OF THE PLASMA-MEMBRANE CA2+-ATPASE ISOFORM PMCA3 IN RAT CEREBELLUM, CHOROID-PLEXUS AND HIPPOCAMPUS

mRNA encoding rat plasma membrane Ca2+-ATPase isoform PMCA3 was localized in the granule cell layer of the cerebellum and in choroid plexus by in situ hybridization with an S-35-labelled oligodeoxynucleotide probe. In order to examine whether this isoform is expressed as a protein in brain, polyclonal antibodies were raised against a peptide corresponding to a C-terminal 18 amino acid sequence of PMCA3 which had been conjugated to bovine serum albumin. Using immunoblot analysis with affinity-purified antibodies, PMCA3 protein was found in rat brain microsomes and cultured neurons. The translated protein had an observed molecular mass of approximately 135 kDa, as predicted from molecular cloning studies. The pattern of localization of PMCA3 in brain using anti-peptide antibodies was consistent with findings from in situ hybridization. PMCA3-like immunoreactive sites were found in the granule cell and molecular layers of rat cerebellum and in choroid plexus, and the pattern of staining suggests that immunoreactive sites are associated with granule cell processes. This conclusion was supported by the finding that growth-associated protein-43, a protein known to be present in axons and nerve terminals, had a pattern of distribution similar to PMCA3 in the molecular layer of cerebellum. Very low levels of PMCA3-like immunoreactivity were associated with Purkinje cell soma or processes, consistent with the low levels of PMCA3 mRNA found in these neurons. PMCA3-like immunoreactivity was lower in hippocampus than in cerebellum; hippocampal CA1 region immunoreactivity was primarily associated with dendritic fields rather than with pyramidal cell bodies. The results demonstrate that a PMCA3-like protein is expressed in neurons of rat brain and is localized primarily in cell processes.