Zonisamide block of cloned human T-type voltage-gated calcium channels.
Zonisamide (ZNS) is a multi-target antiepileptic drug reported to be efficient in the treatment of both partial and generalized seizures, with T-type Ca(2+) channel blockade being one of its proposed mechanisms of action. In this study, we systematically investigated electrophysiological effects of ZNS on cloned human Ca(v)3.1-3.3 Ca(2+) channels in a heterologous HEK-293 expression system using whole cell patch-clamp technique. Concentration-response studies were performed in the range from 5 microM to 2mM for Ca(v)3.2 Ca(2+) channels exhibiting a 15.4-30.8% reduction of Ca(2+) influx within the maximum therapeutic plasma range (50-200 microM ZNS). The other T-type Ca(2+) channel entities, Ca(v)3.1 and Ca(v)3.3, were even less sensitive to ZNS. Both voltage- and concentration-dependence of inactivation kinetics remained unchanged for Ca(v)3.2 VGCC, whereas Ca(v)3.1 and Ca(v)3.3 exhibited minor, though significant reduction of inactivation-tau. Interestingly, ZNS block of Ca(v)3.2 VGCCs was not use-dependent and remained unaffected by changes in the holding potential. Steady-state inactivation studies did not display a significant shift in steady-state availability of Ca(v)3.2 channels at 100 microM ZNS (DeltaV(1/2)=3.1mV, p=0.071). Our studies indicate that ZNS is a moderate blocker of human Ca(v)3 T-type Ca(2+) channels with little or no effect on Ca(v)3.2 Ca(2+) channel inactivation kinetics, use- and state-dependence of blockade. These results suggest that T-type Ca(2+) channel inhibition only partially contributes to the anti-absence activity of ZNS antiepileptic drug.
Matar
Nora
N
Institute of Neurophysiology, University of Cologne, Cologne, Germany.
Jin
Wei
W
Wrubel
Heiko
H
Hescheler
Jürgen
J
Schneider
Toni
T
Weiergräber
Marco
M
D000927:Anticonvulsants / Q000494:pharmacology*; D055592:Biophysical Phenomena / Q000187:drug effects* / Q000235:genetics; D001703:Biophysics; D020747:Calcium Channels, T-Type / Q000235:genetics / Q000378:metabolism; D051244:Caveolin 3 / Q000235:genetics / Q000502:physiology*; D002461:Cell Line, Transformed; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D006801:Humans; D007555:Isoxazoles / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects* / Q000235:genetics; D018408:Patch-Clamp Techniques / Q000379:methods; D014162:Transfection / Q000379:methods; D000078305:Zonisamide
D000927:Anticonvulsants; C121855:CACNA1G protein, human; C479952:CACNA1H protein, human; C469757:CACNA1I protein, human; C417736:CAV3 protein, human; D020747:Calcium Channels, T-Type; D051244:Caveolin 3; D007555:Isoxazoles; D000078305:Zonisamide