Effect of the sulfhydryl reagent thimerosal on cytosolic free Ca 2+ and membrane potential of thymocytes

Abstract

The sulfhydryl reagent thimerosal at concentrations 5–100 μM has been found to induce a variety of changes in ion transport in rat thymocytes. In particular, [Ca 2+] i increases about 10-fold from the basal level. The [Ca 2+] i response to thimerosal displays a two-stage time course, with the main [Ca 2+] i rise during the second stage. Evidence has been obtained for the depletion of intracellular Ca 2+ pools in thimerosal-treated cells, however, Ca 2+ mobilization from intracellular stores does not contribute significantly into [Ca 2+] i rise. Thimerosal elicits permeability not only for Ca 2+, but also for Mn 2+ and Ni 2+, which is Ca 2+-dependent. We failed to get any evidence on thimerosal-induced inhibition of the plasma membrane Ca 2+-ATPase. The induction of Ca 2+ influx, rather than inhibition of Ca 2+-ATPase, accounts for the disturbance of [Ca 2+] i homeostasis in thimerosal-treated cells. Thimerosal also elicits changes in monovalent ion fluxes resulting in marked depolarization. The latter seems unrelated to the changes in [Ca 2+] i and is suggested to be mediated both by increased permeability for Na + and a decreased one for K +. Thimerosal significantly stimulates AA release from thymocytes. Evidence has been presented that AA metabolite(s), probably, LO product(s), may mediate the changes in the transport of mono- and divalent cations elicited by the sulfhydryl reagent. Prolonged treatment of thymocytes with thimerosal resulted in cell death.