EFFECT OF A CARDIOTOXIC COMPONENT OF VENOM OF INDIAN COBRA (NAJA-NIGRICOLLIS) ON SUBCELLULAR STRUCTURE AND FUNCTION OF HEART-MUSCLE

The effect of the purified cardiotoxic component of the venom from the Indian cobra snake (N. nigricollis) on the subcellular function and structure of heart muscle cells was investigated. The concentration of toxin used ranged between 10-50 .mu.g/ml. When added to microsomal fractions rich in sarcoplasmic reticulum 10-50 .mu.g toxin/ml interfered with ability of these fractions to accumulate Ca2+ from an oxalate-containing reaction mixture. This effect was accompanied by an inhibition of the Ca2+-activated ATPase enzyme. Ten, 25 and 50 .mu.g toxin/ml caused the microsomes to release their previously bound Ca2+ at a relatively rapid rate, and accelerated the onset of this release process. Ten .mu.g toxin/ml reduced the ability of isolated mitochondria to accumulate Ca2+ by approximately 50%; the ability of isolated fragments of the plasma membrane to accumulate Ca2+ was also reduced but to a lesser extent. When added to either isolated papillary muscle immersed in Krebs-Henseleit solution or Langendorff-perfused hearts the cardiotoxin caused extensive ultrastructural damage. The plasma membranes were disrupted and particulate matter appeared in the extracellular space. The mitochondria were damaged and contracture bands developed. [Guinea pigs and rabbits were used in this study.].