Extracellular calcium regulates protein tyrosine phosphorylation through calcium-sensing receptor (CaSR) in stallion sperm.

This study examined how extracellular calcium impacts the process of protein tyrosine phosphorylation (PY) in horse sperm cells. It postulates that this is mediated by the presence of calcium-sensing receptors (CaSR), which, when manipulated or blocked, can influence PY, sperm cell motility, and viability.

Introduction

• The research focuses on protein tyrosine phosphorylation, a process recognized as a vital step in sperm cell capacitation, i.e., the final maturation stage that sperm undergo to be capable of fertilizing an egg.
• It was observed that extracellular calcium could potentially inhibit PY in stallion sperm cells.
• This study aimed to identify if a calcium-sensing receptor (CaSR) was present in stallion sperm and to understand its role in mediating this phenomenon.

Methodology

• Initial experiments confirmed the presence of CaSR in the sperm cells.
• The researchers then manipulated the function of these receptors. They used an inhibitor (NPS2143) to prevent their activation, and an agonist (AC34356) to simulate the effect of calcium on these receptors.
• After the sperm were allowed to capacitate for 4 hours under specific conditions, the team then assessed the level of PY.

Results

• The researchers found that the inhibitor NPS2143 could prevent calcium-dependent PY inhibition in a dose-dependent manner.
• The effect of calcium on PY could be replicated by the agonist AC34356.
• It was observed that sperm motility and viability decreased significantly in the presence of high concentrations of the CaSR inhibitor, whereas only sperm motility decrease was noticed with the agonist.
• In the complete absence of calcium, the agonist still inhibited PY but surprisingly led to a significant increase in sperm motility.
• Inhibition of another protein, calmodulin, by a chemical compound called W-7 did not counteract the agonist-mediated PY inhibition.
• Overall, the data suggested that the CaSR plays a vital role in regulating stallion sperm PY, motility, and viability dependent on external calcium conditions, with pH level also being a significant factor.

Conclusion

• This research highlights the critical role of extracellular calcium and CaSR in stallion sperm capacitation, indicating that it could be influential in regulating PY, motility, and viability of sperm cells.
• Understanding the impact of these external conditions on the calcium-sensing receptor’s function could lead to significant advances in animal reproduction science and lend insights into male fertility regulation.