Effects of valproic acid on beta-adrenergic receptors, G-proteins, and adenylyl cyclase in rat C6 glioma cells.

Valproic acid (VPA) is an anticonvulsant drug with demonstrated efficacy in the treatment of mania. In the present study, we found that chronic exposure of rat C6 glioma cells to VPA induces a coordinate decrease in multiple components of the beta-adrenergic receptor- (beta-AR) coupled cyclic adenosine 3'-5'monophosphate (cAMP) generating system. Chronic VPA decreased the number of beta-ARs in a time- and concentration-dependent manner; the decrease of beta-ARs was largely beta 1-AR selective and affected beta-ARs in both the high- and low-affinity states. Chronic VPA also significantly attenuated receptor- and postreceptor-stimulated cAMP production, [3H]forskolin binding sites, immunolabeling of G alpha s 45, and cholera toxin catalyzed ADP-ribosylation of G alpha s 52 and 45. Although the precise underlying mechanisms remain to be elucidated, such profound long-term changes in the functioning of this key signaling pathway may help explain the antimanic effects of chronic VPA treatment and are worthy of further study.