Regulation and roles of Ca(2+) stores in human sperm

[Ca(2) (+)](i) signalling is a key regulatory mechanism in sperm function. In mammalian sperm the Ca(2) (+)-permeable plasma membrane ion channel CatSper is central to [Ca(2) (+)](i) signalling, but there is good evidence that Ca(2) (+) stored in intracellular organelles is also functionally important. Here we briefly review the current understanding of the diversity of Ca(2) (+) stores and the mechanisms for the regulation of their activity. We then consider the evidence for the involvement of these stores in [Ca(2) (+)](i) signalling in mammalian (primarily human) sperm, the agonists that may activate these stores and their role in control of sperm function. Finally we consider the evidence that membrane Ca(2) (+) channels and stored Ca(2) (+) may play discrete roles in the regulation of sperm activities and propose a mechanism by which these different components of the sperm Ca(2) (+)-signalling apparatus may interact to generate complex and spatially diverse [Ca(2) (+)](i) signals.