Dantrolene and mepacrine antagonize the hemolysis of human red blood cells by halothane and bee venom phospholipase A2

Dantrolene is an effective antagonist of anesthesia-induced malignant hyperthermia due to a poorly understood action on skeletal muscle. The present study examines whether the red blood cell can be used as a model to investigate the mechanism of dantrolene action. Halothane (4.7 mM) caused 9% hemolysis of red blood cells. Phospholipase A2 (1 microM) alone caused less than 2% hemolysis, despite high levels (54%) of phosphatidylcholine hydrolysis. Incubation of red blood cells with halothane and phospholipase A2 caused 72% hemolysis. Halothane addition caused 100% hydrolysis of all diacylphosphoglycerides by phospholipase A2, suggesting a mutual potentiation. The major products of phospholipase A2 activity, arachidonic acid and lysophosphatidylcholine, when exogenously added, also greatly increased hemolysis induced by halothane, with arachidonic acid most closely resembling the synergism observed with phospholipase A2. Dantrolene (10 microM) and mepacrine (10 microM) significantly antagonized hemolysis induced by halothane and phospholipase A2 or halothane and exogenously added arachidonic acid and lysophosphatidylcholine. Dantrolene and mepacrine did not antagonize phospholipid hydrolysis or free fatty acid levels. Dantrolene and mepacrine antagonized the synergism between halothane and phospholipase A2 most likely by reducing the lytic action of halothane in the presence of arachidonic acid. The red blood cell is a useful model for studying the antagonism of halothane and phospholipase A2 toxicity by dantrolene and mepacrine.