Effects of lithium on cAMP-dependent protein kinase in rat brain

We have investigated the effects of lithium treatment on cAMP-dependent protein kinase in discrete brain areas of rat by using photoaffinity labeling as well as western blotting. Lithium administered for 5 weeks resulted in a significant increase of the cAMP binding to the 52 kDa cAMP-receptor in the soluble, but not in the particulate, fractions of both hippocampus and frontal cortex. Moreover, immunoblotting experiments revealed that chronic lithium treatment significantly increased the immunoreactivity against the regulatory and the catalytic subunits of the cAMP-dependent protein kinase in the soluble fraction of both brain areas. In contrast, no appreciable effect was observed in the particulate fractions. Short-term lithium treatment induced a significant increase in the immunolabeling of the catalytic subunits in the soluble fraction of both areas; whereas, the regulatory subunits and the actin were unchanged. In the particulate fractions, short-term lithium treatment did not elicit any substantial modification. Taken together, the results of the present study add to the growing evidence indicating that components of the cAMP signalling could play a crucial role in the biochemical action of lithium.