Abstract
Lithium, carbamazepine and sodium valproate are mood stabilizers used in the treatment of bipolar disorder, and although their mechanisms of action remain unknown, signal transduction systems and the associated modulation of gene expression may constitute significant actions. We examined if acute or chronic treatments with these agents modulated the activation of the AP-1 transcription factor or the increased intracellular calcium levels in human neuroblastoma SH-SY5Y cells caused by stimulation with carbachol. AP-1 activation stimulated by carbachol was reduced by pretreatment for 1 h, 24 h or 7 days with 1 mM lithium by 15%, 37%, and 60%, respectively, and with 0.05 mM carbamazepine by 3%, 21%, and 46%, respectively, but not by pretreatment with 0.5 mM sodium valproate. AP-1 DNA binding activity stimulated by carbachol or by phorbol ester-induced activation of protein kinase C was inhibited by the protein kinase C inhibitor Ro31-8220, but phorbol ester-stimulated AP-1 activation was unaltered by 7-day pretreatments with lithium or carbamazepine. Activation of AP-1 by carbachol was dependent on calcium, as it was inhibited by treatment with the extracellular calcium chelator EGTA, the intracellular calcium chelator BAPTA-AM, and the calcium/calmodulin kinase II inhibitor KN62. Pretreatment for 7 days with lithium or carbamazepine had no significant effect on carbachol-stimulated increases in intracellular calcium levels, but reduced the stimulation of AP-1 by the calcium ionophore ionomycin by 30% to 40%. Thus, chronic treatment with the antibipolar agents lithium and carbamazepine attenuates carbachol-stimulated AP-1 DNA binding activity, and these agents preferentially inhibit signaling cascades activated by the calcium rather than the protein kinase C arm of the phosphoinositide signaling pathway.
