Water transport in epididymal and ejaculated rhesus monkey ( Macaca mulatta) sperm during freezing

In the present study, we report the effects of cooling ejaculated and epididymal rhesus monkey ( Macaca mulatta) sperm with and without the presence of a cryoprotective agent, glycerol. Water transport data during freezing of ejaculated and epididymal sperm cell suspensions were obtained at a cooling rate of 20 °C/min in the absence of any cryoprotective agents and in the presence of 0.7 M of glycerol, as well. Using previously published values, the macaque sperm cell was modeled as a cylinder of length 73.83 μm with a radius of 0.40 μm and an osmotically inactive cell volume, V b, of 0.772 V o, where V o is the isotonic cell volume. This translated to a surface area, SA to initial water volume, WV ratio of ∼22 μm −1. By fitting a model of water transport to the experimentally determined volumetric shrinkage data, the best-fit membrane permeability parameters (reference membrane permeability to water at 0 °C, L pg or L pg [ cpa] and the activation energy, E Lp or E Lp [ cpa]) were found to range from: L pg or L pg [ cpa] = 0.0020–0.0029 μm/min-atm; E Lp or E Lp [ cpa]) = 10.6–18.3 kcal/mole. By incorporating these membrane permeability parameters in a recently developed equation (optimal cooling rate, B opt = 1009.5 · exp ( - 0.0546 · E Lp ) · ( L pg ) · ( SA WV ) ; where the units of B opt are °C/min, E Lp or E Lp [ cpa] are kcal/mole, L pg or L pg [ cpa] are μm/min-atm and SA/WV are μm −1), we determined the optimal rates of freezing macaque sperm to be ∼23 °C/min (ejaculated sperm in the absence of CPAs), ∼29 °C/min (ejaculated sperm in the presence of glycerol), ∼24 °C/min (epididymal sperm in the absence of CPAs) and ∼24 °C/min (epididymal sperm in the presence of glycerol). In conclusion, the subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal macaque spermatozoa under corresponding cooling conditions.