Abstract

The main function of mitochondria is the production of ATP through the electron transport chain and lipid oxidation. In addition, this organelle plays an important role in Ca2+ buffering and signaling, shaping and extending the kinetics of Ca2+ signals. Calcium signaling is a key regulatory mechanism in sperm functions such as capacitation, motility, hyperactivation, chemotaxis and acrosome reaction. Progesterone (Pg) has been associated with several processes of sperm physiology, since it directly activates membrane Ca2+ channels. Our group have previously observed that Pg induces an intracellular calcium increase in sperm in media with ≈100nM [Ca2+]. It is unclear which calcium reservoirs of the sperm are involved in this calcium increase. The aim of this study was to investigate the role of mitochondria in calcium signaling involved in the Pg pathway and others functions such as acrosomal reaction and motility parameters in human spermatozoa. To this end, we loaded capacitated human sperm with fluorescent calcium sensor Fluo3-AM, then treated with progesterone in absence or presence of mitochondrial inhibitors in medium containing different [Ca2+]. We used real time dynamic assays with high speed and spatial resolution, in single cells analysis, and computer software to analyze cellular motility parameters. We observed that Pg generated increases of intracellular Ca2+ with particular kinetics and patterns in media with different [Ca2+]. We also noticed that mitochondrial inhibitors altered the Ca2+ patterns and kinetics previously observed. These results suggest that mitochondria participates in calcium signaling in response to Pg.