Chronic ethanol exposure of PC 12 cells after adenylate cyclase activity and intracellular cyclic AMP content

Effects of chronic ethanol exposure on adenylate cyclase activity and intracellular cyclic AMP content were investigated in PC 12 cells. Stimulation of cyclic AMP content by 2-chloroadenosine (2-CADO) and forskolin were reduced after a 4-day exposure of the cells to 150 mM ethanol. Although chronic ethanol treatment did not alter 2-CADO- and NaF-stimulated adenylate cyclase activities in a cell-free preparation, 22-CADO-, forskolin, and NaF-stimulated adenylate cyclase activities were reduced when assays were carried out in saponin-treated cells. Chronic ethanol exposure also increased the ability of in vitro ethanol to stimulate adenylate cyclase activity and cyclic AMP content. The in vitro addition of tert-butanol caused a dose-dependent increase in adenylate cyclase activity, and a 4-day treatment of PC 12 cells with 50 mM tert-butanol reduced 2-CADO- and forskolin-stimulated cyclic AMP contents. Chronic treatment with tert-butanol, however, did not alter the stimulatory effects of in vitro ethanol. Similarly, a 4-day exposure to 125 mM ethanol using serum-free defined media decreased 2-CADO- and forskolin-stimulated cyclic AMP content without changing the stimulatory effects of in vitro ethanol. The increased sensitivity of adenylate cyclase to in vitro ethanol also was not observed when chronic ethanol treatment was carried out with media containing delipidated serum. The increased sensitivity to ethanol, however, was restored when the chronic ethanol treatment was carried out with serum-free defined media supplemented with serum lipoproteins. The present study indicates that chronic ethanol exposure causes heterologous desensitization, but increases the sensitivity of adenylate cyclase to the stimulatory effects of in vitro ethanol. The increased sensitivity to ethanol is not dependent on cyclic AMP, but rather appears to require the presence of exogenous serum lipids.