REGULATION OF NA-ATPASE BY CHRONIC ETHANOL EXPOSURE OF PC-12 CELLS(,K+)

The effects of chronic ethanol exposure on Na+,K+-ATPase were investig ated in PC 12 cells. Inclusion of ethanol in the Na+,K+-ATPase assay ( i.e. in vitro addition of ethanol) inhibited enzyme activity. Converse ly, intrinsic Na+,K+-ATPase activity was increased after chronic ethan ol exposure of the cells. This increase in Na+,K+ pumps occurred witho ut any alteration in the inhibitory effects of in vitro ethanol. A sim ilar response was observed when the chronic treatments were carried ou t using serum-free defined medium. The effects of other agents, which like ethanol decrease membrane order, were investigated. The addition of ketamine and tert-butanol in vitro caused a concentration-dependent inhibition of Na+,K+-ATPase activity. However, chronic exposure of th e PC 12 cells to tert-butanol or ketamine did not alter either intrins ic Na+,K+-ATPase activity or the inhibitory effects of ethanol in vitr o. Maintenance of PC 12 cells in medium containing ethanol resulted in an increase in the intracellular content of Na+ without any change in the K+ levels. In contrast, maintenance of the cells in medium contai ning tert-butanol did not alter intracellular levels of Na+ or K+. The present study shows that the ethanol-induced increase in Na+,K+ pumps involved an increase in the intracellular content of Na+. This increa se in Na+ content did not appear to be secondary to an inhibition of N a+,K+-ATPase activity.