Brain NaK-ATPases in mice differentially sensitive to alcohols

The isozymes of NaK-ATPase were studied in the particulate fraction of homogenates prepared from cortex of LS and SS mice, two lines of mice that have been selectively bred for differential response to ethanol. In addition to a ouabain-insensitive Mg-ATPase, ouabain dose-response curves have suggested the presence, in brain, of two NaK-ATPase activities with different sensitivities to ouabain. These are designated low Ki (4 X 10(-7) M) and high Ki (2 X 10(-4) M). Ethanol differentially inhibited the ATPases: The ouabain-insensitive activity was less sensitive to ethanol inhibition than were the two ouabain-inhibitable activities. The low Ki (brain specific) NaK-ATPase was more sensitive than was the high Ki activity. However, ethanol inhibited all three components of the ATPase activity in an identical fashion in the two mouse lines. The low Ki activity was also more labile to thermal and p-hydroxymercurobenzoate denaturation than was the high Ki activity. These measures did not differ between the LS and SS lines. SDS-polyacrylamide electrophoresis of particulate fraction of cortical homogenates obtained from LS and SS mice revealed the presence of two protein bands with similar 32P labeling in both lines. Given that electrophoretic pattern and heat or p-hydroxymercurobenzoate inhibition were identical, it seems unlikely that differences in ATPase activity, or inhibition by ethanol, are responsible for the different response of LS and SS mice to ethanol.