Concomitant accumulation of intracellular free calcium and arachidonic acid in the ischemic-reperfused rat heart

This study was designed to elucidate the relationship between enhanced cyto plasmic calcium levels (Ca-i(2+)) and membrane phospholipid degradation, a key step in the loss of cellular integrity during cardiac ischemia/reperfus ion-induced damage. Isolated rat hearts were subjected to 15 min ischemia f ollowed by 30 min reperfusion. Ca-i(2+) was estimated by the Indo-1 fluores cence ratio technique. Degradation of membrane phospholipids as indicated b y the increase of tissue arachidonic acid content was assessed in tissue sa mples taken from the myocardium at various points of the ischemia/reperfusi on period. The hemodynamic parameters showed almost complete recovery durin g reperfusion. Fluorescence ratio increased significantly during ischemia, but showed a considerable heart-to-heart variation during reperfusion. Base d upon the type of change of fluorescence ratio during reperfusion, the hea rts were allotted to two separate subgroups. Normalization of fluorescence ratio was associated with low post-ischemic arachidonic acid levels. In con trast, elevated fluorescence ratio coincided with enhanced arachidonic acid levels. This observation is suggestive for a relationship between the Ca2-related fluorescence ratio and arachidonic acid accumulation probably due to a calcium-mediated stimulation of phospholipase A(2).