Effects of milk proteins on sperm binding to the zona pellucida and intracellular Ca(2+) concentration in stallion sperm.

This research studied how milk proteins and calcium levels impact calcium concentrations within stallion sperm cells and how they affect the sperm’s ability to bind to the egg cell’s outer layer. The study found that elevated calcium levels resulted in an increased calcium influx into sperm cells, and specific milk proteins seemed to improve the sperm cells’ binding to the egg cell’s outer layer.

Calcium and Stallion Sperm

• The first experiment focused on the impact of varying levels of calcium, specifically 2mM and 4mM concentrations, on the baseline intracellular calcium concentrations in stallion sperm.
• Sperm cells were treated with ionomycin and incubated for 3 hours. It was found that varying extracellular calcium levels did not affect the baseline intracellular calcium concentration.
• Nevertheless, when sperm cells were incubated in a medium with 4mM calcium as opposed to 2mM calcium, there was a greater influx of calcium into the sperm cells.

Milk Proteins and Stallion Sperm

• The second experiment investigated the effects of milk proteins, specifically native phosphocaseinate (NP) and sodium caseinate (SC), on intracellular calcium concentration and calcium influx in stallion sperm.
• The sperm cells incubated in media containing either NP or SC showed similar baseline intracellular calcium and calcium influx as the control group, which was incubated in Tyrode’s albumin lactate pyruvate (TALP) medium.

Sperm Binding to the Zona Pellucida

• The third experiment focused on whether different proteins, specifically SC, α-casein, β-casein, and κ-casein at different concentrations, affected sperm binding to the zona pellucida (ZP), which is the outer layer of an egg cell.
• It was found that the use of SC increased the number of sperm cells that bound to the bovine ZP, while the use of individual caseins (α-, β- or κ-casein) resulted in similar results to the TALP medium.
• Interestingly, a dose effect was observed for β- and κ-caseins, indicating their possible role in enhancing sperm binding to ZP.

Conclusion

• The experiments concluded that while the extracellular calcium concentration did not affect the baseline intracellular calcium in stallion sperm, a higher calcium concentration did cause an increased calcium influx into the sperm.
• Milk proteins did not significantly affect the baseline intracellular calcium, but β- and κ-caseins were found to possibly enhance sperm binding to the ZP. However, the exact underlying mechanism remains unknown and will need further investigation.