Effect of in vivo changes in phospholipid composition on liver microsomal calcium transport

We recently reported that the phospholipid composition of mouse liver microsomes could be altered in vivo by a combination of dietary choline deprivation and administration of the methylation inhibitors periodate-oxidized adenosine and cycloleucine (D.M. Boyle & W.L. Dean (1982) Biochim. Biophys. Acta 688, 667-670). We have now determined the effect of this in vivo change in phospholipid composition on 7 microsomal enzyme activities and 2 cytochromes. The specific contents of cytochromes b5 and P-450 were unaffected by the treatment. Similarly, NADH-cytochrome c reductase, cytochrome P-450 reductase, cyclohexane hydroxylase and Mg2+-ATPase were not significantly altered. In addition, the phospholipid/protein ratio was not changed. In contrast, Ca2+-ATPase and Ca2+ transport rates were reduced by more than 60%. This result suggests that the mouse liver microsomal Ca2+-ATPase is extremely sensitive to the phospholipid composition of the membrane in which it is embedded and that one mode of control of calcium metabolism in liver cells could be at the level of membrane phospholipid composition.