Effect of the phospholipase A2 inhibitors quinacrine and 7,7-dimethyleicosadienoic acid in isolated globally ischemic rat hearts.

Phospholipase A2 (PLA2) activity results in the formation of lysophospholipids and free fatty acids which may contribute to ischemic myocardial dysfunction. We evaluated the cardioprotective activity of two putative PLA2 inhibitors, quinacrine and 7,7-dimethyleicosadienoic acid (DEDA), in isolated globally ischemic rat hearts. Pretreatment with 1, 5 and 50 microM quinacrine before ischemia did not alter coronary flow but did cause significant cardiodepression. Twenty five minutes of global ischemia and 30 min of reperfusion caused severe myocardial dysfunction and lactate dehydrogenase release. Quinacrine significantly improved reperfusion contractile function and reduced lactate dehydrogenase release, indicative of cardioprotection. In contrast, 30 to 100 microM DEDA produced neither preischemic cardiodepression nor cardioprotective activity. PLA2 inhibition was inferred from measurements of the prostacyclin metabolite, 6-keto-prostaglandin F1 alpha in the coronary effluent and myocardial palmitoyl-lysophosphatidylcholine. Quinacrine and DEDA reduced both 6-keto-prostaglandin F1 alpha and palmitoyl-lysophosphatidylcholine by similar degrees. These results suggest that the cardioprotective activity of quinacrine is independent of PLA2 inhibition. A possible role of calcium inhibition was investigated in rat aortic smooth muscle strips. Norepinephrine-, KCl- and BAY K8644-induced contractions were antagonized in the presence of 5 and 50 microM quinacrine, but were unaffected by 30 to 60 microM DEDA. The ability of quinacrine to inhibit calcium was investigated further in cardiac ventricular myocytes. Measurement of mean whole cell calcium currents showed that quinacrine (5 microM) could inhibit this current up to 70%. Thus, these results suggest that quinacrine-induced cardioprotection may not be due to PLA2 inhibition, but may be related to calcium entry blocking activity.