Studies of Relationships among Bile Flow, Liver Plasma Membrane NaK-ATPase, and Membrane Microviscosity in the Rat

ATPase activity, LPM fluidity, and bile acid-independ-ent flow (BAIF) were studied in rats pretreated with one of five experimental agents. Compared with con-trols, BAIF was increased 24.6 % by thyroid hormone and 34.4 % by phenobarbital, decreased by ethinyl estradiol, but unchanged by propylene glycol and cortisone acetate. Parallel to the observed changes in BAIF, NaK-ATPase activity also was increased by thy-roid hormone (40.8%) and decreased by ethinyl estradiol (26.2%). In contrast, NaK-ATPase activity failed to increase after phenobarbital but did increase 36 % after propylene glycol and 34.8 % after cortisone acetate. Thus BAIF and NaK-ATPase activity did not always change in parallel. The NaK-ATPase Km for ATP was not affected by any of these agents. LPM fluidity, measured by fluorescence polarization using the probe 1,6-diphenyl-1,3,5-hexatriene, was found to be increased by propylene glycol, thyroid hormone, and cortisone acetate, decreased by ethinyl estradiol, and unaffected by phenobarbital. Thus in these cases, induced changes in LPM fluidity paralleled those in NaK-ATPase activity. In no case did Mg-ATPase or 5'-nucleotidase activities change in the same direction as NaK-ATPase, and the activity of neither of these enzymes correlated with LPM fluidity, thus indicating the selective nature of the changes in LPM enzyme activity cauised by the agents