CatSper and the relationship of hyperactivated motility to intracellular calcium and pH kinetics in equine sperm.

The research focuses on understanding equine in-vitro fertilization difficulties by exploring the role of a sperm-specific pH-gated calcium channel, CatSper, and its relationship with sperm motility, intracellular calcium and pH levels. The authors discover that CatSper does exist in equine sperm, yet hyperactivated motility appears weakly tied to calcium influx and independent from procaine’s hyperactivating action.

Research Objectives and Methodology

• The research aims to understand why in vitro fertilization encounters significant problems in horses. Particularly, the researchers question the role of CatSper, a sperm-specific calcium channel, in equine sperm.
• The team utilized computer-assisted sperm motility analysis and fluorescent probes to assess both sperm motility and fluctuations in intracellular pH and calcium levels.
• The presence of a pH-gated calcium channel (presumably CatSper) was confirmed via observed rises in intracellular calcium when pH levels increased, which was hindered by mibefradil, a known CatSper blocker.

CatSper Channel and Its Role

• Hyperactivation in sperm was found to be associated with slight increases in intracellular pH while being inversely proportional to increases in intracellular calcium.
• In a calcium-deficient setting, sperm motility was lost when treated with high-pH, aligning with an influx of sodium through open CatSper channels without environmental calcium present. However, conversely, sperm treated with procaine retained motility and underwent hyperactivation, indicating procaine’s action is not tied to opening the CatSper channel.
• Through PCR testing and immunocytochemistry, CATSPER1 mRNA and CATSPER1 protein were identified in the equine sperm, located in the principal piece of them, revealing the existence of the CatSper channel in equine sperm.

Specified Differences and Conclusions

• By analyzing the predicted equine CATSPER1 protein, the study uncovered species-specific differences in its structure in the pH-sensor region.
• The researchers concluded that while the CatSper channel is indeed present in equine sperm, the link between hyperactivated motility and calcium influx is rather weak.
• The procaine’s initial action of hyperactivating equine sperm doesn’t appear to be influenced by the CatSper channel and it doesn’t rely on external calcium influx.