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 hannah venom had a cardiotoxic action on rat heart. In rats OHV A-PLA2 (2-4 mg/kg) caused ECG abnormalities including decreased heart rate, prolonged P-R interval, widened QRS complex and complete A-V block. When tested on isolated rat right atria, OHV A-PLA2 (10-20 micrograms/ml) produced a positive chronotropic effect. When tested on isolated rat left atria or papillary muscle preparations, OHV A-PLA2 (2.5-20 micrograms/ml) caused positive inotropic effect, followed by contracture. The positive inotropic effects could be abolished by high Ca2+ and enhanced by low Ca2+; both treatments accelerated contracture. The contracture could be inhibited in Mn2+ (5 mM)-containing medium and abolished by Ca(2+)-free bath solution containing 1 mM EDTA. The cardiotoxic action of OHV A-PLA2 was not influenced by verapamil, tetrodotoxin, propranolol, phentolamine, atropine or indomethacin. It is suggested that the cardiotoxic effects of OHV A-PLA2 may result from increasing intracellular levels of Ca2+.
Huang
M Z
MZ
Department of Pharmacology, Fujian Medical College, Fuzhou, P.R. China.
Wang
Q C
QC
Liu
G F
GF
D000758:Anesthesia; D000818:Animals; D001283:Atrioventricular Node / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D004546:Elapid Venoms / Q000037:antagonists & inhibitors / Q000201:enzymology / Q000633:toxicity*; D004562:Electrocardiography / Q000187:drug effects; D005260:Female; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008345:Manganese / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D010210:Papillary Muscles / Q000187:drug effects; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000633:toxicity*; D054467:Phospholipases A2; D051381:Rats; D017208:Rats, Wistar
D004546:Elapid Venoms; D008345:Manganese; D010741:Phospholipases A; D054467:Phospholipases A2; D008274:Magnesium; D002118:Calcium