Influence of sulfhydryl reagents on potassium-stimulated calcium uptake by rat brain synaptosomes.

Potassium-stimulated calcium uptake by rat brain synaptosomes was measured by placing synaptosomes in a high (70 mM) potassium medium containing 45Ca. K+-stimulated uptake was essentially complete within 20 s. K+-stimulated calcium uptake was inhibited by pretreating the synaptosomes with N-ethylmaleimide, a sulfhydryl alkylating reagent. Methylmercury chloride and mercuric chloride inhibited K+-stimulated calcium uptake in the same concentration ranges at which they formed complexes with surface sulfhydryl groups. Ethylmercury chloride was considerably less effective at inhibiting calcium uptake and reacting with sulfhydryl groups. The presence of essential sulfhydryl moieties in the structures subserving K+-stimulated calcium uptake by nerve terminals is suggested.