Changes in physicochemical properties of lipid membranes extracted from mitochondria during the formation process of megamitochondria induced by hydrazine.

Changes in some biochemical and physicochemical properties of lipid membranes extracted from rat liver mitochondria during the formation process of megamitochondria induced by hydrazine were analyzed. Hepatic mitochondria obtained from rats placed on a 1% hydrazine diet for 3 days became slightly enlarged while they became gigantic after 7 days of hydrazine intoxication. Changes were distinct in mitochondria of rats treated with hydrazine for 3 days : 1) Among phospholipid species, relative amounts of phosphatidylethanolamine (PE), phosphatidylserine (PS) and lysophosphatidylcholine (LPC) were increased. A ratio of cholesterol to phospholipid and that of unsaturated to saturated fatty acids were increased. 2) Contents of Ca2+ in mitochondria were increased. 3) Differential scanning calorimetric analysis of lipid membranes extracted from mitochondria showed that the thermotropic lipid phase transition temperatures were elevated. The values of enthalpy were increased and were smaller in the presence of Ca2+ than those in the absence of Ca2+. 4) The fluidity of those membranes was increased by the addition of Ca2+.These changes had a tendency to return to nomal after 7 days of hydrazine treatment. The result described in #3 was reproduced using PS-PC mixture. From the above described data the bilayer structure in the mitochondrial membranes during the process of megamitochondrial formation might possibly be destabilized by PS-Ca2+ and PE-cholesterol interactions. These results would suggest that the membrane fusion might be involved in the megamitochondrial formation.