Stimulation of sodium and calcium uptake by scorpion toxin in chick embryo heart cells |
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Authors: | François Couraud Hervé Rochat Serge Lissitzky |
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Affiliation: | 1. Laboratoire de Biochimie Médicale et U 38 de l''Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine, 27 Bd. Jean-Moulin, 13385 Marseille Cédex 4 France;2. Laboratoire de Biochimie, Faculté de Médecine, Secteur Nord, Bd. Pierre Dramard, 13326 Marseille Cédex 3 France |
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Abstract: | Scorpion toxins, the basic miniprotiens of scorpion venom, stimulated the passive uptake of Na+ and Ca2+ in chick ermbryo heart cells. Half-maximum stimulation was obtained for 20–30 nM Na+ and 40–50 nM Ca2+. Scorpion toxin-activated Na+ and Ca2+ uptakes were fully inhibited by tetrodotoxin, a specific inhibitor of the action potential Na+ ionophore in excitable membranes. Half-maximum inhibition was obtained with the same concentration of tetrodotoxin (10 nm) for both Na+ and Ca2+. Scorpion toxin-stimulated Ca2+ uptake was dependent on extracellular Na+ concentration and was not inhibited by Ca2+ channel blocking drugs which are inactive on heart cell action potential. Thus, in heart cells scorpion toxin affects the passive Ca2+ transport, which is coupled to passive Na+ ionphore. Other results suggest that (1) tetrodotoxin and scorpion toxin bind to different sites of the sarcolemma and (2) binding of scorpion toxin to its specific sites may unmask latent tetrodotoxin — sensitive fast channels. |
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Keywords: | HEPES |
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