Abstract
Spatial and temporal control of intracellular calcium signaling is essential for neuronal development and function. The termination of local Ca^2+^ signaling and the maintenance of basal Ca^2+^ levels require specific extrusion systems in the plasma membrane. In rat hippocampal neurons (HNs) developing in vitro, transcripts for all isoforms of the plasma membrane Ca^2+^ pump and the Na/Ca^2+^ exchanger, and the major nonphotoreceptor Na^+^/Ca^2+^,K^+^ exchangers (NCKX) were strongly upregulated during the second week in culture. Upregulation of plasma membrane calcium ATPases (PMCAs)1, 3, and 4 mRNA coincided with a splice shift from the ubiquitous bโtype to the neuronโspecific aโtype with altered calmodulin regulation. Expression of all PMCA isoforms increased over 5โfold during the first 2 weeks. PMCA immunoreactivity was initially concentrated in the soma and growth cones of developing HNs. As the cells matured, PMCAs concentrated in the dendritic membrane and often colocalized with actinโrich dendritic spines in mature neurons. In the developing rat hippocampal CA1 region, immunohistochemistry confirmed the upregulation of all PMCAs and showed that by the end of the second postnatal week, PMCAs1, 2, and 3 were concentrated in the neuropil, with less intense staining of cell bodies in the pyramidal layer. PMCA4 staining was restricted to a few cells showing intense labeling of the cell periphery and neurites. These results establish that all major Ca^2+^ extrusion systems are strongly upregulated in HNs during the first 2 weeks of postnatal development. The overall increase in Ca^2+^ extrusion systems is accompanied by changes in the expression and cellular localization of different isoforms of the Ca^2+^ pumps and exchangers. The accumulation of PMCAs in dendrites and dendritic spines coincides with the functional maturation in these neurons, suggesting the importance of the proper spatial organization of Ca^2+^ extrusion systems for synaptic function and development. ยฉ 2005 WileyโLiss, Inc.