Selective blockade of N-type calcium channels by levetiracetam.
OBJECTIVE
We investigated the effect of the new antiepileptic drug (AED) levetiracetam (LEV) on different types of high-voltage-activated (HVA) Ca2+ channels in freshly isolated CA1 hippocampal neurons of rats.


METHODS
Patch-clamp recordings of HVA Ca2+ channel activity were obtained from isolated hippocampal CA1 neurons. LEV was applied by gravity flow from a pipette placed near the cell, and solution changes were made by electromicrovalves. Ca2+ channel blockers were used for separation of the channel subtypes.


RESULTS
The currents were measured in controls and after application of 1-200 microM LEV. LEV irreversibly inhibited the HVA calcium current by approximately 18% on the average. With a prepulse stimulation protocol, which can eliminate direct inhibition of Ca2+ channels by G proteins, we found that G proteins were not involved in the pathways underlying the LEV inhibitory effect. This suggested that the inhibitory effect arises from a direct action of LEV on the channel molecule. The blocking mechanism of LEV was not related to changes in steady-state activation or inactivation of Ca2+ channels. LEV also did not influence the rundown of the HVA Ca2+ current during experimental protocols lasting approximately 10 min. Finally, LEV at the highest concentration used (200 microM) did not influence the activity of L-, P- or Q-type Ca2+ channels in CA1 neurons, while selectively influencing the activity of N-type calcium channels. The maximal effect on these channels separated from other channel types was approximately 37%.


CONCLUSIONS
Our results provide evidence that LEV selectively inhibits N-type Ca2+ channels of CA1 pyramidal hippocampal neurons. These data suggest the existence of a subtype of N-type channels sensitive to LEV, which might be involved in the molecular basis of its antiepileptic action.
Lukyanetz
E A
EA
Bogomoletz Institute of Physiology, Kiev, Ukraine. elena@serv.biph.kiev.ua
Shkryl
V M
VM
Kostyuk
P G
PG
D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004827:Epilepsy / Q000503:physiopathology*; D006624:Hippocampus / Q000166:cytology; D007700:Kinetics; D000077287:Levetiracetam; D009474:Neurons / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010889:Piracetam / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D000927:Anticonvulsants; D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D000077287:Levetiracetam; D009543:Nifedipine; D010889:Piracetam; D020866:omega-Conotoxin GVIA