Effect of pentabarbital dependence on adenylate cyclase activity and calmodulin levels in rat cerebral cortex

The effect of calcium (Ca²⁺) on the adenylate cyclase activity and calmodulin level of cerebral cortex was determined in pentobarbital dependent rats and age matched controls. Female Sprague-Dawley rats were made dependent and maintained on pentobarbital by eating a mixture of pentobarbital and rat chow (350 mg pentobarbital/30 g chow). Ca²⁺ activated then inhibited the adenylate cyclase activity associated with a 20,000 x g particulate fraction from pentobarbital dependent and age matched control rats. The values for one-half maximal stimulation and inhibition by Ca²⁺ did not differ significantly in either cortical preparation. However, the ability of Ca²⁺ to activate adenylate cyclase from pentobarbital dependent animals was significantly decreased (p<0.05) when compared to control animals. Pentobarbital (10^-4 - 10^-3) added to particulate fractions from naive control rats did not alter the ability of Ca²⁺ to activate adenylate cyclase. The calmodulin levels in the particulate fraction from pentobarbital dependent animals (30.2 ± 6.7 ng calmodulin/mg protein) did not differ significantly when compared to control (33.0 ± 4.7 ng/mg). By contrast, the calmodulin levels (37.9 ± 5.9 ng/mg) in the 20,000 x g supernatant from cortex of pentobarbital dependent animals was significantly greater than the level in the supernatant from control animals (28.6 ± 2.6 ng/mg). The ability of forskolin, dopamine, GTP or forskolin plus GTP (all at a concentration of 100 μM) to activate adenylate cyclase was significantly decreased in particulate preparations from pentobarbital dependent animals. In summary, our data show that alterations in calmodulin levels and a decreased responsivity of adenylate cyclase occur in animals physically dependent on pentobarbital.