Pharmacology of scorpion toxin II in the skeletal muscle

Scorpion (Odontobuthus doriae) venom induces apoptosis and inhibits DNA synthesis in human neuroblastoma cells

Scorpion and its organs have been used to cure epilepsy, rheumatism, and male impotency since medieval times. Scorpion venom which contains different compounds like enzyme and non-enzyme proteins, ions, free amino acids, and other organic inorganic substances have been reported to posses antiproliferative, cytotoxic, apoptogenic, and immunosuppressive properties. We for the first time report the apoptotic and antiproliferative effects of scorpion venom (Odontobuthus doriae) in human neuroblastoma cells. After exposure of cells to medium containing varying concentrations of venom (10, 25, 50, 100, and 200 μg/ml), cell viability decreased to 90.75, 75.53, 55.52, 37.85, and 14.30%, respectively, after 24 h. Cells expressed morphological changes like swelling, inhibition of neurite outgrowth, irregular shape, aggregation, rupture of membrane, and release of cytosolic contents after treatment with venom. Lactate dehydrogenase (LDH) level increased in 50 and 100 μg/ml as compared to control, but there was no significant increase in LDH level at a dose of 10 and 20 μg/ml. Two concentrations viz. 50 and 100 μ/ml were selected because of the profound effect of these concentrations on the cellular health and population. Treatment with these two concentrations induced reactive nitrogen intermediates and depolarization in mitochondria. While caspase-3 activity increased in a concentration-dependent manner, only 50 μg/ml was able to fragment DNA. It was interesting to note that at higher dose, i.e., 100 μg/ml, the cells were killed, supposedly by acute necrosis. DNA synthesis evidenced by bromodeoxyuridine (BrdU) incorporation was inhibited in a concentration-dependent manner. The cells without treatment incorporated BrdU with high affinity confirming their cancerous nature whereas very less incorporation was noticed in treated cells. Our results show apoptotic and antiproliferative potential of scorpion venom (O. doriae) in human neuroblastoma cells. These properties make scorpion venom a valuable therapeutic agent in cancer research.

A comparison of the actions of cobra cardiotoxin and scorpion toxin II on the guinea-pig taenia coli

Both cobra cardiotoxin (CTX) and scorpion toxin II induce contracture of the guinea-pig taenia coli, the latter being more potent than the former. Tachyphylaxis was observed with each toxin. Acetylcholine (ACh) contracture was enhanced by toxin II but not by CTX. High K+ (152 mM) abolished toxin II contracture but only partially inhibited CTX and ACh contractures. Ca2+-free medium, especially in the presence of 1 mM EGTA, inhibited CTX- and toxin II-contracture by more than 60%, but abolished ACh contracture. On the other hand, high Ca2+ (12 mM) was without effect on ACh contracture but inhibited both CTX- and toxin II-contracture, and enhanced K+ contracture. Contracture was produced after washout of Ca2+-free medium and toxins but not after washout of high Ca2+ medium, suggesting that the binding of toxins was inhibited by high Ca2+. Tetrodotoxin (TTX) abolished toxin II contracture, but only partially inhibited CTX contracture. Atropine markedly inhibited toxin II contracture but did not significantly affect CTX contracture. Procaine potentiated CTX contracture but abolished toxin II contracture. The spontaneous contraction induced by toxin II was also inhibited by TTX, atropine and procaine. ACh contracture was abolished by atropine and potentiated by procaine, but unaffected by TTX. The rate of decline of K+ (60 mM) contracture in Ca2+-free medium was enhanced by CTX but unaffected by toxin II. 45Ca2+ efflux was increased by CTX more than by toxin II. Both toxins also significantly increased 45Ca2+ uptake. These findings indicate that CTX induces contracture of taenia coli mainly by releasing the Ca2+ pool of the muscle membrane, whereas toxin II does so mainly by releasing acetylcholine from nerve terminals and partially by acting on the muscle membrane as a result of an increase of the membrane Na+ permeability.

Mode of stimulatory actions of cadmium ion on the mouse diaphragm

Effects of Cd2+ on the phrenic nerve-diaphragm preparation of the mouse varied markedly in media containing various Ca2+ concentrations. In normal 2.5 mM Ca2+ medium, Cd2+ inhibited acetylcholine release from nerve endings without appreciable effect on the muscle membrane. However, Cd2+ elicited stimulatory effects on the muscle membrane in low Ca2+ medium (10(-3)-1 mM). These stimulatory effects included the induction of spontaneous contractions, augmentation of twitch responses to direct electrical stimulation and potentiation of the muscle contracture induced by acetylcholine, carbachol and high K+. By contrast, caffeine contracture was not affected by Cd2+. Tetrodotoxin, procaine, cysteine and glycerol pretreatment abolished these stimulatory effects of Cd2+. Moreover, changing the ionic composition of the bathing medium to one containing low Na+, high K+, high Mg2+ or high Ca2+ also antagonized these effects of Cd2+. In contrast, low Mg2+ markedly potentiated the frequency of spontaneous contractions induced by Cd2+. (+)-Tubocurarine and beta-bungarotoxin had no effect on Cd2+-induced spontaneous contractions indicating that they may be myogenic rather than neurogenic in origin. By use of conventional microelectrodes, it was found that Cd2+ not only depolarized the muscle membrane but also induced spontaneous action potentials at a high frequency (173 +/- 17 Hz). It is concluded that increased Na+ permeability of the muscle membrane is the essential step bringing about spontaneous contractions. The binding of Cd2+ to -SH groups of the membrane is closely related to the induction of these effects.