The Antiepileptic Drug Levetiracetam Decreases the Inositol 1,4,5-Trisphosphate-Dependent [Ca2+]i Increase Induced by ATP and Bradykinin in PC12 Cells
- Division of Pharmacology, Department of Neuroscience, School of Medicine, Federico II University of Naples, Naples, Italy
- Address correspondence to:
Dr. Lucio Annunziato, Division of Pharmacology, Department of Neuroscience, Federico II University of Naples, Via Pansini no. 5, 80131 Naples, Italy. E-mail: lannunzi{at}unina.it
Abstract
The present study explores the hypothesis that the new anti-epileptic drug levetiracetam (LEV) could interfere with the inositol 1,4,5-trisphosphate (IP3)-dependent release of intracellular Ca2+ initiated by Gq-coupled receptor activation, a process that plays a role in triggering and maintaining seizures. We assessed the effect of LEV on the amplitude of [Ca2+]i response to bradykinin (BK) and ATP in single Fura-2/acetoxymethyl ester-loaded PC12 rat pheochromocytoma cells, which express very high levels of LEV binding sites. LEV dose-dependently reduced the [Ca2+]i increase, elicited either by 1 μM BK or by 100 μM ATP (IC50, 0.39 ± 0.01 μM for BK and 0.20 ± 0.01 μM for ATP; Hill coefficients, 1.33 ± 0.04 for BK and 1.38 ± 0.06 for ATP). Interestingly, although the discharge of ryanodine stores by a process of calcium-induced calcium release also took place as part of the [Ca2+]i response to BK, LEV inhibitory effect was mainly exerted on the IP3-dependent stores. In fact, the drug was still effective after the pharmacological blockade of ryanodine receptors. Furthermore, LEV did not affect Ca2+ stored in the intracellular deposits since it did not reduce the amplitude of [Ca2+]i response either to thapsigargin or to ionomycin. In conclusion, LEV inhibits Ca2+ release from the IP3-sensitive stores without reducing Ca2+ storage into these deposits. Because of the relevant implications of IP3-dependent Ca2+ release in neuron excitability and epileptogenesis, this novel effect of LEV could provide a useful insight into the mechanisms underlying its antiepileptic properties.
Footnotes
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This work was partially supported by a grant from UCB Pharma (Braine-L'Alleud, Belgium). This work was also supported by Grant PRIN 2002 from the Ministero Italiano per l' Università e la Ricerca Scientifica (to L.A.); by Grant PNR 2001-2003-FIRB art. 8 D. M. 199 (to L.A.); by POP and Legge 41/94 from Regione Campania, annualità 98 (to L.A.); by Programma Speciale art. 12bis comma 6, D. Lgs. 229/99 from Ministero della Salute and Regione Campania (to L.A.); by Progetto di Ricerche Finalizzato, Convenzione Ministero della Salute/Regione Campania, no. 1, 1 dicembre 2003 (to L.A.); and by POR 2006, asse 3, misura 3.16, from Centro Regionale di Competenza di Genomica Funzionale, Genomics for Applied Research (to L.A.). V.L. is a Ph.D. student supported by a fellowship grant from the Centro Regionale di Competenza di Genomica Funzionale, Genomics for Applied Research.
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doi:10.1124/jpet.104.079327.
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ABBREVIATIONS: LEV, levetiracetam; AED, antiepileptic drug; IP3, inositol 1,4,5-trisphosphate; BK, bradykinin; AM, acetoxymethyl ester; TG, thapsigargin; AUC, area under the curve; ANOVA, analysis of variance; Rya, ryanodine; Iono, ionomycin; CICR, calcium-induced calcium release; RyR, ryanodine receptor.
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- Received October 17, 2004.
- Accepted January 7, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
