Abstract
We have reported that a transient treatment of hippocampal neurons with alpha-tocopherol induced a long-lasting protection against oxidative damage mediated by Fe(2+) ions. This protection required protein synthesis. Here, we have studied whether this "hyposensitivity" to oxidative stress could be linked to an altered Ca(2+) homeostasis. Fe(2+) ions triggered a Ca(2+) entry which was required for Fe(2+) ion-induced toxicity. This influx was sensitive to blockers of TRP-like nonspecific Ca(2+) channels, including Ruthenium Red, La(3+), and Gd(3+) ions which also prevented the Fe(2+) ion-induced toxicity and oxidative stress as revealed by protein carbonylation status. The pretreatment with alpha-tocopherol resulted in a reduction of the Ca(2+) increase induced by Fe(2+) ions and masked the blocking effect of La(3+) ions. Moreover, such a pretreatment reduced the capacitive Ca(2+) entries (CCE) observed after metabotropic glutamate receptor stimulation, which are known to involve TRP-like channels. By contrast, in a model of "hypersensitivity" to oxidative stress obtained by chronic stimulation of glucocorticoid receptors, we observed an exacerbation of the various effects of Fe(2+) ions, i.e., cellular toxicity and Ca(2+) increase, and the glutamate-stimulated CCE. Therefore, we conclude that the long-lasting neuroprotection induced by alpha-tocopherol pretreatment likely results from an attenuation of Ca(2+) entries via TRP-like channels.