Chronic ethanol ingestion increases calcium uptake and resistance to molecular disordering by ethanol in liver microsomes.

Calcium uptake and molecular ordering were studied in hepatic microsomes from rats treated chronically with ethanol and were compared with the effects of ethanol in vitro. Calcium uptake was increased by 30% in microsomes from ethanol-fed animals, the Vmax being increased and the Km remaining unchanged. In Arrhenius plots of calcium uptake, the transition temperature in the 25-30 degrees C range was higher by 1.5 degrees C in microsomes from ethanol-fed rats. Chronic ethanol administration resulted in more rigid microsomal membranes, as evidenced by EPR spectra of the spin probe 5-doxylstearic acid. In a plot of the order parameter, S, as a function of temperature, microsomes from ethanol-fed rats showed a discontinuity at a higher temperature than those from controls (29.9 versus 24.2 degrees C). Ethanol, in vitro, inhibited microsomal calcium uptake in both preparations. However, the degree of inhibition was greater in controls. The rate of calcium uptake by microsomes from ethanol-treated animals in the presence of 100 mM ethanol was the same as those from controls in the absence of ethanol. In vitro, increasing concentrations of ethanol progressively decreased molecular ordering of control microsomes, whereas little change was noted in microsomes after chronic ethanol treatment.