L-type Ca2+ channel blockers attenuate electrical changes and Ca2+ rise induced by oxygen/glucose deprivation in cortical neurons.
OBJECTIVE
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 not 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 (O2)/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% N2/5% CO2 gas mixture.


RESULTS
Eight to twelve minutes of O2/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 [Ca2+]i levels. When O2/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 O2/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 O2/glucose deprivation.
Pisani
A
A
Clinica Neurologica, Dipartimento di Sanitá, Universitá Tor Vergata, and Ospedale S. Lucia, IRCCS, Rome, Italy. pisani@utovrm.it
Calabresi
P
P
Tozzi
A
A
D'Angelo
V
V
Bernardi
G
G
D000818:Animals; D002545:Brain Ischemia / Q000378:metabolism* / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000145:classification / Q000494:pharmacology*; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects; D003592:Cytophotometry; D003620:Dantrolene / Q000494:pharmacology; D004734:Energy Metabolism; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D005947:Glucose / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D017966:Pyramidal Cells / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018691:Excitatory Amino Acid Antagonists; D005456:Fluorescent Dyes; D013779:Tetrodotoxin; D009553:Nimodipine; D003620:Dantrolene; D009543:Nifedipine; D005947:Glucose; D002118:Calcium; D016257:Fura-2