Stimulation of sodium and calcium uptake by scorpion toxin in chick embryo heart cells.
Scorpion toxins, the basic miniproteins of scorpion venom, stimulated the passive uptake of Na+ and Ca2+ in chick embryo 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.
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011526:Protoveratrines / Q000494:pharmacology; D012605:Scorpions; D012964:Sodium / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D014118:Toxins, Biological / Q000494:pharmacology*
D011526:Protoveratrines; D014118:Toxins, Biological; D013779:Tetrodotoxin; D010042:Ouabain; D012964:Sodium; D011433:Propranolol; D002118:Calcium