Membrane phase behavior during cooling of stallion sperm and its correlation with freezability.

This research investigates if the varying survival rate of stallion sperm after cryopreservation (freezing) is due to differences in the membrane phase and permeability properties. Using Fourier transform infrared spectroscopy, the researchers find that although individual stallions exhibit significant differences in post-thaw progressive motility, and other factors, these properties did not clearly differ in relation to sperm freezability.

Research Method and Key Findings

• The researchers collected sperm samples from stallions that have displayed varying degrees of sperm viability after undergoing cryopreservation, a method for preserving cells by freezing.
• A molecule analysis technique known as Fourier transform infrared spectroscopy (FTIR) was used to determine the membrane phase transitions at both above and below zero temperatures, thus unveiling the characteristic sub-zero membrane hydraulic permeability parameters.
• The research showed that stallion sperm undergoes a slow and expansive membrane phase transition at temperatures above zero, specifically from 30°C to 10°C. However, a more dramatic change in phase transition takes place when the cells are dehydrated through freezing which forces them into a highly ordered gel phase.
• The results indicated significant differences between individual stallions in terms of post-thaw progressive motility (which is a measure of the movement of sperm cells), percentages of sperm cells with abnormal morphology, and chromatin stability (which measures DNA integrity). Despite these differences, there was no clear distinction between these biophysical properties and the differences in sperm freezability (the survival rate after freezing) among the stallions.

Impact of Treatments on Membrane Phase Transitions

• The study also explored the effects of removing cholesterol from cellular membranes via cyclodextrin treatment. This method increased the coordination of the suprazero phase transition, but did not significantly alter the subzero membrane phase behavior.
• Protective agents were used during freezing to study their effects. It was observed that they slow down the rate of membrane dehydration, thus increasing the extent of dehydration.
• Moreover, these cryoprotective agents, such as glycerol, also reduce the quantity of energy required to transport water across cell membranes during freezing, thereby potentially enhancing the freezing process.

In summary, the study identifies potential factors impacting the survival rate of stallion sperm post-cryopreservation but suggests no definitive correlation between these biophysical properties and the differences in sperm freezability among stallions.