EFFECT OF THIMEROSAL AND OTHER SULFHYDRYL-REAGENTS ON CALCIUM PERMEABILITY IN THYMUS LYMPHOCYTES

We have studied the effects of thimerosal, a mercurial compound extens ively used as a preservative, as well as other sulfhydryl reagents (e. g. p-hydroxymercurybenzoate, hydrogen peroxide, bromophenacyl bromide, and mercuric chloride) on Ca2+ homeostasis and the redox status of su lfhydryl groups in thymus lymphocytes. They all induced an increase in [Ca2+](i) which was blocked with dithiothreitol, suggesting that they act via the oxidation or blockade of sulfhydryl groups. [Ca2+](i) inc rease could be directly related to the effect of the different reagent s on cellular protein sulfhydryl content. Experiments with ethidium br omide indicate that the observed rise in [Ca2+](i) was not due to a no n-specific increase in membrane permeability. Thimerosal differs from the other agents studied in its oxidative properties, which is probabl y linked to the production of a potent reductor molecule, thiosalicyli c acid, which may modulate its oxidative capacity.