The thiol reagent, thimerosal induces intracellular calcium oscillations in mature human oocytes

The aim of this study was to investigate the effects of thimerosal on intracellular calcium in human oocytes related to the stage of nuclear maturity. A total of 20 oocytes from superovulated women undergoing gamete intra-Fallopian transfer (GIFT) were studied. The calcium-sensitive fluorescent dye Fura-2 was used to monitor intracellular calcium. Regular oscillations in the concentration of cytosolic calcium were observed in 13 out of 20 oocytes following exposure to thimerosal; five oocytes did not respond to thimerosal treatment, and spontaneous oscillations of cytosolic free calcium were recorded in two oocytes. Thimerosal induced oscillations of intracellular calcium in a significantly higher proportion of metaphase II oocytes (10/11) compared with metaphase I oocytes (3/8; P < 0.2). These findings demonstrate that thimerosal is a potentially useful agent for the study of the calcium signalling processes in human eggs and suggest that the underlying cellular mechanisms develop at a relatively late stage of oocyte maturation.