Further Studies on Physicochemical Properties of Mitochondrial Membranes during the Formation Process of Megamitochondria in the Rat Liver by Hydrazine

Abstract Physicochemical properties of lipids extracted from hepatic mitochondria of rats fed with 1% hydrazine diet for 3 days (3H-mitochondria) and 7 days (7H-mitochondria) were studied using differential scanning calorimetry and the fluorescence polarization measurements. Results obtained from lipids extracted from 3H-mitochondria were as follows: (1) Thermotropic phase transition temperatures ( T m ) were elevated with a distinct increase in transition enthalpy (Δ H ) compared to those of the control due to increases in relative amounts of phosphatidylethanolamine (PE) and phosphatidylserine (PS) in phospholipid species. (2) T m in lipids and phospholipids extracted from 3H-mitochondria was elevated with decreases in Δ H after the addition of Ca 2+ , whereas Δ H of the control was increased after the addition of Ca 2+ . (3) Phosphatidylcholine (PC) liposomes containing PE or PS at concentrations corresponding to PE/PC or PS/PC ratio in 3H-mitochondria showed elevations of transition temperatures with decreases in Δ H values after the addition of Ca 2+ , whereas those containing PE or PS ratio at concentrations corresponding to PE/PC or PS/PC in the control mitochondria showed increases in Δ H values after the addition of Ca 2+ . (4) There were essentially no changes in membrane fluidity between lipids extracted from 3H-mitochondria and those extracted from the control mitochondria. Addition of Ca 2+ to lipids extracted from 3H-mitochondria, however, caused elevation of membrane fluidity while those extracted from the control mitochondria showed no changes in membrane fluidity after the addition of Ca 2+ . (5) Increases in the ratio of unsaturated fatty acids to saturated fatty acids ( U/S ratio) in phospholipids extracted from 3H-mitochondria were found to be mainly due to those in PS. These data may suggest that hydrazine modifies the membrane of mitochondria favorable for the membrane fusion via enhanced acidic phospholipid-Ca 2+ interactions.