Figure 1.

Ca²⁺ channels and pumps that have been immunolocalized in mammalian sperm. Arrows indicate the most common direction of Ca²⁺ movement caused by these entities in most cell types. The chief channels and pumps involved in hyperactivation are CatSper channels and PMCA, which are indicated by large arrows. Others that have been identified include the following: sarcoplasmic/endoplasmic reticular Ca²⁺ ATPase (SERCA), IP₃-gated channels (IP3); voltage-operated Ca²⁺channels (VOCC), TRPC Ca²⁺ channels, secretory pathway Ca²⁺ ATPase (SPCA), NCX, mitochondrial uniporter (MCU) and CNG Ca²⁺ channels.