Na⁺/Ca²⁺exchanger 3 (NCX3), one of the three isoforms of the NCX family, is highly expressed in the brain and is involved in the maintenance of intracellular Na⁺and Ca²⁺homeostasis. Interestingly, whereas the function of NCX3 under physiological conditions has been determined, its role under anoxia is still unknown. To assess NCX3 role in cerebral ischemia, we exposed ncx3−/− mice to transient middle cerebral artery occlusion followed by reperfusion. In addition, to evaluate the effect of ncx3 ablation on neuronal survival, organotypic hippocampal cultures and primary cortical neurons from ncx3−/− mice were subjected to oxygen glucose deprivation (OGD) plus reoxygenation. Here we report that ncx3 gene suppression leads to a worsening of brain damage after focal ischemia and to a massive neuronal death in all the hippocampal fields of organotypic cultures as well as in cortical neurons from ncx3−/− mice exposed to OGD plus reoxygenation. In addition, in ncx3−/− cortical neurons exposed to hypoxia, NCX currents, recorded in the reverse mode of operation, were significantly lower than those detected in ncx3+/+. From these results, NCX3 protein emerges as a new molecular target that may have a potential therapeutic value in modulating cerebral ischemia.

In the current study, the potential blocking ability of K⁺channels encoded by the human ether-a-go-go related gene (HERG) by the piperazine H₁ receptor antagonist cetirizine has been examined and compared with that of other second-generation antihistamines (astemizole, terfenadine, and loratadine). Cetirizine was completely devoid of any inhibitory action on HERG K⁺ channels heterologously expressed inXenopus laevis oocytes in concentrations up to 30 μm. On the other hand, terfenadine and astemizole effectively blocked HERG K⁺ channels with nanomolar affinities (the estimated IC₅₀ values were 330 and 480 nm, respectively), whereas loratadine was ∼300-fold less potent (IC₅₀ ≈ 100 μm). In addition, in contrast to terfenadine, cetirizine did not show use-dependent blockade. In SH-SY5Y cells, a human neuroblastoma clone that constitutively expresses K⁺ currents carried by HERG channels (I_HERG), as well as in human embryonic kidney 293 cells stably transfected with HERG cDNA, extracellular perfusion with 3 μm cetirizine did not exert any inhibitory action on I_HERG. Astemizole (3 μm), on the other hand, was highly effective. Terfenadine (3 μm) caused a marked (≈80%) inhibition of I_HERG in SH-SY5Y cells, whereas loratadine, at the same concentration, caused a 40% blockade. Furthermore, the application of cetirizine (3 μm) on the intracellular side of the membrane of HERG-transfected human embryonic kidney 293 cells did not affect I_HERG, whereas the same intracellular concentration of astemizole caused a complete block. The results of the current study suggest that second-generation antihistamines display marked differences in their ability to block HERG K⁺ channels. Cetirizine in particular, which possesses more polar and smaller substituent groups attached to the tertiary amine compared with other antihistamines, lacks HERG-blocking properties, possibly explaining the absence of torsade de pointes ventricular arrhythmias associated with its therapeutical use.

Changes in intracellular [Ca²⁺]_i levels have been shown to influence developmental processes that accompany the transition of human oligodendrocyte precursor cells (OPCs) into mature myelinating oligodendrocytes and are required for the initiation of the myelination and re-myelination processes. In the present study, we explored whether calcium signals mediated by the selective sodium calcium exchanger (NCX) family members NCX1, NCX2, and NCX3, play a role in oligodendrocyte maturation. Functional studies, as well as mRNA and protein expression analyses, revealed that NCX1 and NCX3, but not NCX2, were divergently modulated during OPC differentiation into oligodendrocyte phenotype. In fact, whereas NCX1 was downregulated, NCX3 was strongly upregulated during oligodendrocyte development. The importance of calcium signaling mediated by NCX3 during oligodendrocyte maturation was supported by several findings. Indeed, whereas knocking down the NCX3 isoform in OPCs prevented the upregulation of the myelin protein markers 2′,3′-cyclic nucleotide-3′-phosphodiesterase (CNPase) and myelin basic protein (MBP), its overexpression induced an upregulation of CNPase and MBP. Furthermore, NCX3-knockout mice showed not only a reduced size of spinal cord but also marked hypo-myelination, as revealed by decrease in MBP expression and by an accompanying increase in OPC number. Collectively, our findings indicate that calcium signaling mediated by NCX3 has a crucial role in oligodendrocyte maturation and myelin formation.

Human ether-a-gogo related gene (HERG) K⁺channels are key elements in the control of cell excitability in both the cardiovascular and the central nervous systems. For this reason, the possible modulation by reactive oxygen species (ROS) of HERG and other cloned K⁺channels expressed inXenopusoocytes has been explored in the present study. Exposure ofXenopusoocytes to an extracellular solution containing FeSO₄(25–100 μM) and ascorbic acid (50–200 μM) (Fe/Asc) increased both malondialdehyde content and 2′,7′-dichlorofluorescin fluorescence, two indexes of ROS production. Oocyte perfusion with Fe/Asc caused a 50% increase of the outward K⁺currents carried by HERG channels, whereas inward currents were not modified. This ROS-induced increase in HERG outward K⁺currents was due to a depolarizing shift of the voltage-dependence of channel inactivation, with no change in channel activation. No effect of Fe/Asc was observed on the expressed K⁺currents carried by other K⁺channels such as bEAG, rDRK1, and mIRK1. Fe/Asc-induced stimulation of HERG outward currents was completely prevented by perfusion of the oocytes with a ROS scavenger mixture (containing 1,000 units/ml catalase, 200 ng/ml superoxide dismutase, and 2 mM mannitol). Furthermore, the scavenger mixture also was able to reduce HERG outward currents in resting conditions by 30%, an effect mimicked by catalase alone. In conclusion, the present results seem to suggest that changes in ROS production can specifically influence K⁺currents carried by the HERG channels.