Sodium valproate at therapeutic concentrations changes Ca2+ response accompanied with its weak inhibition of protein kinase C in human astrocytoma cells

Sodium valproate (VPA) has been used clinically for treatment of not only epilepsy but also mood disorder. Although VPA is effective for treatment of epilepsy via inhibition of gamma-aminobutyfic acid transaminase, it remains unknown why VPA is effective for the treatment of mood disorder. The authors examined the effect of VPA at therapeutic concentrations (300 and 600 mu M) on the elevation of intracellular free calcium concentration ([Ca2+](i)) induced by carbachol, a muscarinic receptor agonist, in 132 IN I human astrocytoma cells. Treatment of the cells with 300 and 600 pM VPA for 2 min did not change the carbacholl-induced [Ca2+](i) elevation. Treatment with 300 and 600 mu M VPA for 48 h, however, reduced the elevation. Since we have shown that Li+ reduced carbachol-induced [Ca2+](i) elevation in protein kinase C (PKC)-downregulated 1321N1 cells [Kurita, M., Mashiko, H., Rai, M., Kumasaka, T., Kouno, S., Niwa, S., Nakahata, N., 2002. Lithium chloride at a therapeutic concentration reduces Ca2+ response in protein kinase C down-regulated human astrocytoma cells, Eur. J. Pharmacol. 442, 17-22.], the activity of PKC was examined. Treatment with VPA at the same concentrations for 24 or 48 It weakly reduced protein kinase C activity in membrane and cytosol ftactions from the cells. On the other hand, the treatment of the cells with 600 mu M VPA for 24 or 48 h slightly increased the B-max value, but not the K-d value, in the binding of [H-3]quinuclidinyl benzylate, a muscarinic receptor ligand, to the membranes, suggesting that the number or affinity of muscarinic receptor did not decrease after VPA treatment. These results indicate that VPA at therapeutic concentrations slightly decreases the PKC activity and inhibits muscarinic receptor-mediated [Ca2+](i) elevation probably through change in the intracellular signaling pathway. VPA-induced reduction of PKC activity and [Ca2+](i) elevation may play a role in the treatment of mood disorder. (c) 2007 Published by Elsevier Inc.