Inhibition of permeability-dependent Ca2+ release from mitochondria by N-acylethanolamines, a class of lipids synthesized in ischemic heart tissue.

Abstract

are shown here to inhibit the development of increased inner membrane permeability in heart mitochondria produced by Ca2+ plus Ca2+-releasing agents such as oxalacetate, N-ethylmaleimide, and palmitoyl coenzyme A. The inhibition is concentrationdependent, requiring approximately 30 p~ for a halfmaximal effect with N-oleoylethanolamine. Higher levels of this compound inhibit energy-dependent Ca2+ accumulation, maximal rates of succinate oxidation and the development of membrane potential.Half-maximal effects for these activities are seen at approximately 120 p ~. Inhibition of Ca2+ uptake appears to be a secondary consequence of inhibited energy production rather than an effect on the Ca2+ uniporter per se.Inhibition of succinate oxidation is noncompetitive with respect to succinate concentration, suggesting that this activity arises at the level of electron transport.N-Acylethanolamine has analogous actions on liver mitochondria except that 2to %fold lower concentrations are required to inhibit energy production.In addition, at lower levels, a stimulation rather than inhibition of Ca2+-dependent permeability increase is observed.This difference is due to the action of a hydrolase degrading the amide linkage, an enzyme which is present in liver but not in heart mitochondria.The resulting accumulation of free fatty acids in liver mitochondria can lead to the synthesis of intramitochondrial acylcoenzyme A which increases the sensitivity to Ca2+ and other Ca2+-releasing agents.A survey of tissue homogenates revealed that hydrolysis of N-oleoylethanolamine occurs most rapidly in liver but does not occur in heart.Considering the actions of N-acylethanolamine on mitochondria and the requirements for the biosynthesis of these compounds, it is concluded that they could function to protect cells subjected to ischemic insult and perhaps to injury by other agents which