Plasma membrane Na؉ /Ca 2؉ -exchangers play a predominant role in Ca 2؉ extrusion in brain. Neurons express several different Na ؉ /Ca 2؉ -exchangers belonging to both the K ؉ -independent NCX family and the K ؉ -dependent NCKX family. The unique contributions of each of these proteins to neuronal Ca 2؉ homeostasis and/or physiology remain largely unexplored. To address this question, we generated mice in which the gene encoding the abundant neuronal K ؉ -dependent Na ؉ /Ca 2؉ -exchanger protein, NCKX2, was knocked out. Analysis of these animals revealed a significant reduction in Ca 2؉ flux in cortical neurons, a profound loss of long term potentiation and an increase in long term depression at hippocampal Schaffer/CA1 synapses, and clear deficits in specific tests of motor learning and spatial working memory. Surprisingly, there was no obvious loss of photoreceptor function in cones, where expression of the NCKX2 protein had been reported previously. These data emphasize the critical and non-redundant role of NCKX2 in the local control of neuronal [Ca 2؉ ] that is essential for the development of synaptic plasticity associated with learning and memory.

] c elevations mediated by NCX alone, and NCX plus NCKX combined, were 17 and 6 times more rapid in FNs than in CGCs, respectively. Northern blot analysis showed that FNs preferentially express NCX1 whereas CGCs expressed NCX3. Differences in expression of other isoforms (NCX2, NCKX2, NCKX3 and NCKX4) were less pronounced. We tested whether the NCX or NCKX family of exchangers contributes most to the toxic NMDA-induced Ca 2+ influx in depolarized neurons. We found that in FNs, inhibition of NCX alone was sufficient to significantly limit NMDA excitotoxicity, whereas in CGCs, inhibition of both NCX and NCKX was required. The data suggest that the high activity of NCX isoforms expressed in FNs, possibly NCX1, sensitizes these neurons to NMDA excitotoxicity.

, and K ϩ homeostasis in the CNS, the role of NCKX2 during cerebral ischemia, a condition characterized by an alteration of ionic concentrations, has not yet been investigated. The present study examines NCKX2 role in the development of ischemic brain damage in permanent middle cerebral artery occlusion (pMCAO) and transient middle cerebral artery occlusion. Furthermore, to evaluate the effect of nckx2 ablation on neuronal survival, nckx2؊/؊ primary cortical neurons were subjected to oxygen glucose deprivation plus reoxygenation. NCKX2 mRNA and protein expression was evaluated in the ischemic core and surrounding ipsilesional areas, at different time points after pMCAO in rats. In ischemic core and in periinfarctual area, NCKX2 mRNA and protein expression were downregulated. In addition, NCKX2 knock-down by antisense oligodeoxynucleotide and NCKX2 knock-out by genetic disruption dramatically increased infarct volume. Accordingly, nckx2؊/؊ primary cortical neurons displayed a higher vulnerability and a greater [Ca 2ϩ ] i increase under hypoxic conditions, compared with nckx2؉/؉ neurons. In addition, NCKX currents both in the forward and reverse mode of operation were significantly reduced in nckx2؊/؊ neurons compared with nckx2؉/؉ cells. Overall, these results indicate that NCKX2 is involved in brain ischemia, and it may represent a new potential target to be investigated in the study of the molecular mechanisms involved in cerebral ischemia.

Numerous isoforms of plasmalemmal K-dependent (NCKX) and K-independent (NCX) Na+/Ca2+ exchangers are expressed in the brain. The physiological functions of each isoform are presently unknown. Therefore, in this study, we compared expression of NCKX and NCX transcripts between primary cultures of cerebellar granule cells, and astrocytes. Northern blot analysis showed that granule cells expressed NCKX2, NCKX3, NCKX4 and NCX3, whereas astrocytes expressed primarily NCX1. Consistent with this molecular characterization, a significant fraction of 45Ca2+ accumulation in Na-loaded granule cells, but not in astrocytes, depended on external K+. This is the first demonstration of native NCKX activity in neurons derived from the central nervous system. Our data suggest that NCKX isoform expression may correspond to the unique Ca2+ homeostasis requirements of neurons.