L-Type Ca 2+ Channel Blockers Attenuate Electrical Changes and Ca 2+ Rise Induced by Oxygen/Glucose Deprivation in Cortical Neurons

Abstract

Background and Purpose —Experimental evidence supports a major role of increased intracellular calcium [Ca 2+ ] i levels in the induction of neuronal damage during cerebral ischemia. However, the source of Ca 2+ rise has not been fully elucidated. To clarify further the role and the origin of Ca 2+ 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 [Ca 2+ ] i were performed simultaneously in slices perfused with a glucose-free physiological medium equilibrated with a 95% N 2 /5% CO 2 gas mixture. Results —Eight to twelve minutes of O 2 /glucose deprivation induced an initial membrane hyperpolarization, followed by a delayed, large but reversible membrane depolarization. The depolarization phase was accompanied by a transient increase in [Ca 2+ ] i levels. When O 2 /glucose deprivation exceeded 13 to 15 minutes, both membrane depolarization and [Ca 2+ ] i rise became irreversible. The dihydropyridines nifedipine and nimodipine significantly reduced either the membrane depolarization or the [Ca 2+ ] 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 [Ca 2+ ] i accumulation. Finally, dantrolene, blocker of intracellular Ca 2+ release, did not reduce both electrical and [Ca 2+ ] i changes caused by O 2 /glucose depletion. Conclusions —This work supports a role of L-type Ca 2+ channels both in the electrical and ionic changes occurring during the early phases of O 2 /glucose deprivation.