Calcium Influx and Male Fertility in the Context of the Sperm Proteome: An Update

Figure 1

Possible signal transduction mechanisms of mammalian sperm Ca²⁺ influx through the Ca²⁺ permeable channel proteins. Previously published studies were used as references to summarize the list of channel proteins in spermatozoa. The channel proteins are localized mainly in the principle piece of spermatozoa. The follicular fluid and several factors in the fallopian tube (in vitro media) stimulate the receptors for spermatozoa Ca²⁺ influx. Ca²⁺ influx in spermatozoa is principally regulated by CatSper channels; however, the possible interaction between other channels that are responsible for controlling the opening of CatSper and allowing the Ca²⁺ into cells is indicated by arrow signs (red circle). The different channel proteins that are depicted in the diagram include the Na⁺-coupled HCO₃⁻ transporter (NBC) family, soluble adenylyl cyclase (sACY), adenosine triphosphate (ATP), cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), cyclic nucleotide-gated ion channel (CNG), hyperpolarization-activated cyclic nucleotide-gated channel (HCN), zona pellucida (ZP), the voltage-gated proton channel (Hv1), glutamate receptor family class-C (GPCRC), and an unknown mechanism (?).