Carnosine is a known protector of neuronal cells against oxidative injury which prevents both apoptotic and necrotic cellular death. It was shown earlier that carnosine serves as an intracellular buffer of free radicals. Using the model of ligand-dependent oxidative stress in neurons, we have shown that homocysteine (HC) initiates long-term activation of extracellular signal regulated kinase, isoforms 1 and 2 (ERK 1/2) and Jun N-terminal kinase (JNK) which corresponds to exitotoxic effect resulting in cellular death. L-carnosine (β-alanyl-L-histidine) protects neurons from both excitotoxic effect of homocysteine and cellular death. Its analogs, β-alanyl-D-histidine (D-carnosine) and L-histidyl-β-alanine, restricted accumulation of free radicals and delayed activation of ERK1/2 and JNK in neuronal cells, but did not promote neuronal viability.

Inhibition of rat neuronal Na(+)/K(+)-ATPase alpha3 isoform at low (100 nM) ouabain concentration led to activation of MAP kinase cascade via PKC and PIP(3) kinase. In contrast to ouabain-sensitive alpha3 isoform of Na(+)/K(+)-ATPase, an ouabain-resistant alpha1 isoform (inhibition with 1 mM of ouabain) of Na(+)/K(+)-ATPase regulates MAP kinase via Src kinase dependent reactions. Using of Annexin V-FITC apoptotic test to determine the cells with early apoptotic features allows to conclude that alpha3 isoform stimulates and alpha1 suppresses apoptotic process in cerebellum neurons. These data are the first demonstration showing participation of ouabain-resistant (alpha1) and ouabain-sensitive (alpha3) Na(+)/K(+)-ATPase isoforms in diverse signaling pathways in neuronal cells.

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Using SK‐N‐AS human neuroblastoma cells, which co‐express the α1 and α3 isoforms of the sodium pump α subunit, we selectively silenced either the α1 or α3 subunit by means of transfection with small interfering RNA, and investigated cell survival and the cellular response to ouabain. We found that both of the α subunits are essential for cell survival, indicating that substitution of one subunit for the other is not sufficient. In the presence of both α subunits, ouabain causes sustained activation of extracellular signal‐regulated kinases 1 and 2 (Erk1/2). This activation is not affected when the α1 subunit is silenced. However, when α3 expression is silenced, ouabain‐induced activation of Erk1/2 does not occur, even at a high concentration of ouabain (1 μm). Thus, ouabain‐induced Erk1/2 activation is mediated in SK‐N‐AS cells by α3 only, and α1 does not participate in this event. This is a clear demonstration of selective involvement of a specific sodium pump α subunit isoform in ouabain‐induced signaling.