The effect of scorpion venom tityustoxin on the uptake of calcium in synaptosomes

The effect of tityustoxin on calcium uptake in synaptosomes incubated in hypotonic medium low sodium and physiological medium high sodium was studied. In the hypotonic medium, calcium uptake was ATP and temperature dependent and TsTX inhibits this uptake. The inhibition of calcium uptake was not due to an osmotic effect since it was also observed in conditions of physiological cell osmolarity. In the physiological medium high sodium, tityustoxin stimulated calcium uptake in synaptosomes. The effect was inhibited by tetrodotoxin and cocaine. The stimulating effect of tityustoxin was specific for sodium concentration in the medium and neither choline nor sucrose could substitute sodium in its activation of the stimulation of calcium uptake in synaptosomes by tityustoxin.