Regulation and roles of Ca2+ 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.