Background: Adenylyl cyclase (AC) activity is increased in the presence of ethanol. The magnitude of ethanol's action on AC depends on the isoform of AC expressed in a particular cell type. Type VII AC demonstrates the greatest potentiation of activity in the presence of ethanol, but questions have arisen regarding the effects of pharmacologically relevant (approximately 50 mM) concentrations of ethanol on type VII AC activity. Questions also remain as to whether the potentiation of AC activity by ethanol initiates downstream effects on protein kinase A activity.
Methods: HEK293 (human embryonic kidney 293) cells overexpressing type VII AC were used to study the dose-dependent actions of ethanol on cyclic adenosine monophosphate (cAMP) production. Studies were performed in the presence and absence of phosphodiesterase inhibitors. Protein kinase A activity was assessed under conditions similar to those used to measure ethanol's actions on AC.
Results: A significantly greater percent stimulation of prostaglandin E1-mediated cAMP accumulation was evident in the absence of the phosphodiesterase inhibitors 3-isobutyl-1-methylxanthine and Ro 20-1724 than in the presence of the phosphodiesterase inhibitors. We also showed that ethanol was not, itself, acting as a phosphodiesterase inhibitor. The calculated percent stimulation of AC activity by ethanol depended on the baseline levels of cAMP production in the absence of ethanol. In the absence of 3-isobutyl-1-methylxanthine (or other phosphodiesterase inhibitors), a 50 mM concentration of ethanol produced a 56% increase in prostaglandin E1-stimulated cAMP production in the type VII AC transfected HEK293 cells. This concentration of ethanol also produced a significant activation of protein kinase A beyond that produced by prostaglandin E1 alone.
Conclusions: The present study indicates that, in the presence of a particular isoform of AC, moderately intoxicating concentrations of ethanol will significantly potentiate the transmitter-mediated activation of the cAMP signaling cascade. Activation of this signaling cascade may have important implications for the mechanisms by which ethanol produces intoxication and/or in the mechanisms of neuroadaptation leading to tolerance to, and physical dependence on, ethanol.