Structural requirements of lysophospholipid-regulated mitochondrial Ca2+ transport

Analogues of lysophosphatidylcholine, including PAF (platelet-activating-factor) and HePC (an experimental anticancer drug), were studied for their influence on mitochondrial Ca2+ transport and membrane potential. Lysophospholipids released Ca2+ from mitochondria and reduced the maximal Ca2+ uptake. The structure-activity relations indicate that deprotonated head groups like phosphocholines yield active compounds while partially protonated head groups like phosphoethanolamines are essentially inactive. Structural requirements for the apolar part of the molecules were acyl or alkyl chain lengths of less than 18 carbon atoms at the C1-position of the glycerol backbone and residues of small size and/or low polarity at the C2-position. Choline lysophospholipids, but not ethanolamine lysophospholipids, may therefore induce mitochondrial Ca2+ efflux and become mediators of ischaemic tissue damage where dysregulated phospholipase A2 activity and an impairment of mitochondrial function are supposed to play a crucial role.