L-type Ca2+ channel blockers attenuate electrical changes and Ca2+ rise induced by oxygen/glucose deprivation in cortical neurons

Background and Purpose-Experimental evidence supports a major role of increased intracellular calcium [Ca2+](i) levels in the induction of neuronal damage during cerebral ischemia. However, the source of Ca2+ rise has trot been fully elucidated. To clarify further the role and the origin of Ca2+ in cerebral ischemia, we have studied the effects of various pharmacological agents in an in vitro model of oxygen (O-2)/glucose deprivation. Methods-Pyramidal cortical neurons were intracellularly recorded from a slice preparation. Electrophysiological recordings and microfluorometric measurements of [Ca2+](i) were performed simultaneously in slices perfused with a glucose-free physiological medium equilibrated with a 95% N-2/5% CO2 gas mixture. Results-Eight to twelve minutes of O-2/glucose deprivation induced all initial membrane hyperpolarization, followed by a delayed, large but reversible membrane depolarization. The depolarization phase was accompanied by a transient increase in [Ca2+](i) levels. When O-2/glucose deprivation exceeded 13 to 15 minutes, both membrane depolarization and [Ca2+](i) rise became irreversible. The dihydropyridines nifedipine and nimodipine significantly reduced either the membrane depolarization or the [Ca2+](i) elevation. In contrast, tetrodotoxin had no effect on either of these parameters. Likewise, antagonists of ionotropic and group I and II metabotropic glutamate receptors failed to reduce the depolarization of the cell membrane and the [Ca2+](i) accumulation. Finally, dantrolene, blocker of intracellular Ca2+ release, did not reduce both electrical and [Ca2+](i) changes caused by O-2/glucose depletion. Conclusions-This work supports a role of L-type Ca2+ channels both in the electrical and ionic changes occurring during the early phases of O-2/glucose deprivation.