EXPRESSION, DISTRIBUTION, AND ACTIVITY OF NA-ATPASE IN NORMAL AND CHOLESTATIC RAT-LIVER(,K+)

Hepatocellular Na+,K+-ATPase is an important driving force for bile se cretion and has been localized to the basolateral plasma membrane doma in. Cholestasis or impaired bile flow is known to modulate the express ion, domain specificity, and activity of various transport systems inv olved in bile secretion. This study examined Na+,K+-ATPase after ethin ylestradiol (EE) treatment and after bile duct ligation (BDL), two rat models of cholestasis. It applied quantitative immunoblotting, bioche mical and cytochemical determination of enzyme activity, and immunocyt ochemistry to the same livers. The data showed a good correlation amon g the results of the different methods. Neither EE nor BDL induced alt erations in the subcellular distribution of Na+,K+-ATPase, which was f ound in the basolateral but not in the canalicular (apical) plasma mem brane domain. Protein expression and enzyme activity showed a small (s imilar to 10%) decrease after EE treatment and a similar increase afte r BDL. These modest changes could not be detected by immunofluorescenc e, immune EM, or cytochemistry. The data, therefore, demonstrate that Na+,K+-ATPase is only slightly affected by EE and BDL. They suggest th at other components of the bile secretory apparatus that take effect d ownstream of the primary basolateral driving force may play a more pro minent role in the pathogenesis of cholestasis.