CARDIOLIPIN-PROTEIN COMPLEXES AND INITIATION OF COMPLEMENT ACTIVATIONAFTER CORONARY-ARTERY OCCLUSION

Specific rabbit anti-cardiolipin (anti-CL) antibodies were used to inv estigate the hypothesis that cardiolipin, associated with mitochondria l membrane proteins, binds C1 and facilitates activation of the comple ment cascade following reperfusion of ischemic myocardium. By immunoel ectron microscopy, anti-CL localized to subsarcolemmal mitochondria, e merging through breaks in membranes of damaged cardiac myocytes. Anti- CL reacted with >15 mitochondrial constituents, most of which comigrat ed with the proteins that bind C1q in transblots of subsarcolemmal mit ochondria, fractionated by polyacrylamide gel electrophoresis under re ducing conditions in the presence of sodium dodecyl sulfate. A subset of the C1q-binding proteins >24 to 37 kD served as stable sites for as sembly of C3, C5, and C9. Cardiac lymph, collected during the first ho ur after reperfusion of ischemic myocardium, contained proteins of div erse size that reacted with both anti-CL and C1q. Cardiac lymph, colle cted before occlusion and 4 to 5 hours after reperfusion, in compariso n, had few if any C1q or anti-CL reactive proteins. Treatment with pho spholipase suppressed the C1q-binding activity and anti-CL reactivity of the proteins in reperfusion lymph and those with similar properties in mitochondrial extracts. Our data suggest that during ischemia, mit ochondria, extruded through breaks in the sarcolemma, unfold and relea se membrane fragments in which cardiolipin and protein are intimately associated. By binding C1 and supplying sites for the assembly of late r-acting complement components, these fragments provide the means to d isseminate the complement-mediated inflammatory response to ischemic i njury.