ELEVATING INTRACELLULAR CALCIUM LEVELS IN HUMAN SPERM USING AN INTERNAL CALCIUM-ATPASE INHIBITOR, 2,5-DI(TERT-BUTYL) HYDROQUINONE (TBQ), INITIATES CAPACITATION AND THE ACROSOME REACTION BUT ONLY IN THE PRESENCE OF EXTRACELLULAR CALCIUM

The aim of this study was to investigate the effect of an internal cal cium ATPase inhibitor, TBQ, on human sperm capacitation and the acroso me reaction during incubation in a calcium-depleted media. Sperm were isolated into and incubated for up to 6 hr in media depleted of Ca2+ a nd two Ca2+-containing media controls. At set time intervals, sperm in each media group were treated with 100 mu M TBQ for 5 min. Afterwards , sperm were induced to acrosome react using the divalent cation ionop hore, A23187, as a measure of sperm fertilizing potential. It was esta blished, using the Chlortetracycline assay, that incubation of sperm i n a Ca2+-depleted media inhibited or delayed sperm capacitation result ing in fewer spontaneous or A23187-induced acrosome reacted sperm. How ever, incubation of sperm in a Ca2+-depleted media did not appear to i nhibit sperm motility. The treatment of sperm with TBQ during their in cubation in Ca2+-depleted media was found to have very little effect r esulting in low numbers of capacitated and acrosome reacted sperm. The results from this study suggest that human sperm have an obligatory r equirement for extracellular calcium during capacitation and the acros ome reaction, but may require either very little extracellular Ca2+ to maintain motility or possess internal Ca2+ stores sufficient for thei r requirements. In addition, TBQ did not increase the number of capaci tated and acrosome reacted sperm during incubation in a Ca2+-depleted media suggesting that the TBQ-effect of accelerating sperm capacitatio n is dependent on presence of extracellular Ca2+. (C) 1997 Wiley-Liss, Inc.