DUAL ACTIVATION OF THE DAMAGE SYSTEM THAT CAUSES THE RELEASE OF CYTOSOLIC PROTEINS IN THE PERFUSED RAT-HEART

Caffeine (10 mM) or 2,4-dinitrophenol (DNP; 1 mM) caused release of cr eatine kinase (CK) in the perfused rat heart but only when previously activated by Ca-0(2+) depletion, Simultaneous Ca-0(2+) depletion and c affeine or DNP perfusion markedly reduced CK release. Activation by Ca -0(2+) depletion was inhibited at 28 degrees C. Both the Ca2+ paradox and caffeine-induced release of CK were inhibited by 1 mM amiloride, P erfusion of anoxic standard medium lacking glucose had no overt effect s, but CK release began immediately on subsequent Ca2+ depletion. A sm all, but steady release of CK was observed after glucose-free, anoxic perfusion for 75 min. CK release produced by reoxygenation after anoxi a (the O-2 paradox) is augmented if anoxic perfusion is lengthened fro m 20 to 45 min. The Ca2+ paradox is markedly inhibited by 2 mM iodoace tate (IAA), even when this is introduced after Ca-0(2+) depletion. Sin ce caffeine or DNP caused ultrastructural damage in the presence of ex tracellular Ca2+ (when no CK was released) it is concluded that the pa thways of myofilament degradation and CK release can be independently activated, It is concluded that CK release is synergistically triggere d by removal of extracellular Ca2+ and a rise in [Ca2+](i). It is sugg ested that Ca-0(2+) depletion causes membrane perturbation that activa tes a trans-sarcolemma complex that is critically dependent on its mob ility within the bilayer, is intimately linked to a Na+/H+ antiporter and is inhibited by IAA.