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KMID : 0903519960390030189
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Journal of the Korean Society of Agricultural Chemistry and Biotechnology
1996 Volume.39 No. 3 p.189 ~ p.194
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Scorpion Venom Activates Both Ca2+ - ATPase and Inositol 1,4,5 - trisphosphate Receptor in the Microsomes of Tracheal Epithelial Cells
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Abstract
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The effects of scorpion (Leiurus quinquestriatus hebraeus, Lqh) venom were evaluated on the activities of microsomal Ca^(2+)-ATPase and Ca^(2+) release channel prepared from the epithelial cells of pig airway. Whole venom of Lqh (120 ㎍/㎖) increased the activity of microsomal Ca^(2+)-ATPases about 32% in the tight-sealed microsomes and about 28% in the Triton X-100-treated or Ca^(2+) ionophore A23187-treated leaky microsomes. Thapsigargin, a specific antagonist of Ca^(2+)-ATPase, inhibited 42% of total ATPase activity and also completely blocked the effects of Lqh venom, suggesting that Lqh venom directly activates the microsomal Ca^(2+)-ATPases. In order to determine if Lqh venom increases the microsomal uptake of ^(45)Ca^(2+), Lqh venom was added in the uptake medium. The Lqh venom increased microsomal ^(45)Ca^(2+) uptake up to ∼20% and the increase was only observed when heparin, an antagonist of InsP₃ receptor channel, was added in the uptake medium. Lqh venom in the absence of heparin unexpectedly decreased the rate and the amount of ^(45)Ca^(2+) uptake. These results were explained by simultaneous increases in ^(45)Ca^(2+) release as well as ^(45)Ca^(2+) uptake by Lqh venom. Lqh venom itself increased the release of ^(45)Ca^(2+) as much as ^(45)Ca^(2+) release by 4 μM InsP₃, implying that Lqh venom also activates InsP₃ receptor, microsomal Ca^(2+) release channel. Based on these results, we suggest that the Lqh venom consists of at least two components; one activates the InsP₃ receptor and the other activates the Ca^(2+)-ATPase. Currently we are investigating the chemical and electrophysiological properties of the active components of Lqh venom.
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