The Phospholipase A2Induced Increase in the Permeability of Phospholipid Membranes to Ca2⊕and H⊕Ions

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Abstract
The permeability of liposomes prepared from beef heart mitochondrial phospholipids was studied after treatment with phospholipase A2. The permeability to H+ ions was measured by recording the rate of change of pH in the external medium following an addition of an aliquot of alkali to liposomes with a highly buffered inner medium, while the penetration of Ca2+ ions into liposomes was measured in liposomes loaded with arsenazo III. There was a doubling of H+ permeability when the lysophospholipid content was increased to 2% by treatment with phospholipase A2, and a tripling at 4%. Entrapped sucrose leakage from liposomes became apparent at about 6% lysophospholipid. Treatment with phospholipase A2 stimulated Ca2+ penetration into liposomes driven by a valinomycin-induced diffusion potential or a negericin-induced H+ gradient. The data are discussed in relation to the mechanism of damage to mitochondria occurring in Ca2+ overload as well as in phospholipase A2-induced cellular damage.

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