Activation of protein kinase A is necessary but not sufficient for ethanol-induced desensitization of cyclic AMP production
Acute addition of EtOH to PC 12 pheochromocytoma cells increases cyclic AMP production, whereas chronic exposure to EtOH results in a decrease in the stimulation of cyclic AMP production in response to 2-chloroadenosine and forskolin. This EtOH-induced desensitization was not observed after chronic EtOH treatment of A126-1B2-1 cells which are a protein kinase A-deficient mutant cell line derived from PC 12 cells. Furthermore, in the parental PC 12 cell line the cell-permeable protein kinase A inhibitor, Rp-isomer of adenosine 3',5'-monophosphorothioate, blocked the development of EtOH-induced desensitization. Thus, activation of protein kinase A is apparently necessary for EtOH-induced desensitization of cyclic AMP production. Chronic treatment of PC 12 cells with forskolin qualitatively mimicked the desensitization observed with chronic EtOH exposure. However, the degree of desensitization induced by forskolin was significantly less than that caused by EtOH even though the acute addition of forskolin caused a greater increase in cyclic AMP production. Furthermore, the acute addition of EtOH inhibited forskolin-stimulated cyclic AMP production, yet inclusion of EtOH during the chronic forskolin treatment of PC 12 cells resulted in a greater degree of desensitization. These findings indicate an obligatory role of protein kinase A in EtOH-induced desensitization of cyclic AMP production in PC 12 cells. However, because protein kinase A activation alone is not sufficient to account for the degree of desensitization, EtOH probably also acts through a mechanism in addition to activation of protein kinase A.