EFFECTS OF AN ACIDIC PHOSPHOLIPASE-A2 PURIFIED FROM OPHIOPHAGUS-HANNAH (KING COBRA) VENOM ON RAT-HEART

An acidic phospholipase A2 (OHV A-PLA2) purified from Ophiophagus hann ah venom had a cardiotoxic action on rat heart. In rats OHV A-PLA2 (2- 4 mg/kg) caused ECG abnormalities including decreased heart rate, prol onged P-R interval, widened QRS complex and complete A-V block. When t ested on isolated rat right atria, OHV A-PLA2 (10-20 mug/ml) produced a positive chronotropic effect. When tested on isolated rat left atria or papillary muscle preparations, OHV A-PLA2 (2.5-20 mug/ml) caused p ositive inotropic effect, followed by contracture. The positive inotro pic effects could be abolished by high Ca2+ and enhanced by low Ca2+; both treatments accelerated contracture. The contracture could be inhi bited in Mn2+ (5 mM)-containing medium and abolished by Ca2+-free bath solution containing 1 mM EDTA. The cardiotoxic action of OHV A-PLA2 w as not influenced by verapamil, tetrodotoxin, propranolol, phentolamin e, atropine or indomethacin. It is suggested that the cardiotoxic effe cts of OHV A-PLA2 may result from increasing intracellular levels of C a2+.