A comparison of critical osmolality and hydraulic conductivity and its activation energy in fowl and bull spermatozoa.

Measurements were made of critical osmolality, the osmolality at which 50% of the cells are lysed, and of the permeation time, the time taken to lyse 50% of the cells in an osmotic solution lower than the critical osmolality, for fowl and bull spermatozoa. Cell lysis was determined by means of fluorescent viability stains (carboxyfluorescein diacetate and propidium iodide) using a flow cytometer. The advantages and pitfalls of this approach are addressed. The values obtained have been used to compute the water permeability, or hydraulic conductivity, of the plasma membrane and its activation energy for each species. Fowl spermatozoa were found to have a lower critical osmolality (17 mOsm) than bull spermatozoa (36 mOsm), and this is discussed in relation to the differences in cell shape and size. The hydraulic conductivities of fowl and bull spermatozoa were 2.1 and 10.8 microns x atmosphere x minute, respectively, and the respective activation energies were 4.4 and 3.0 kcal/mol. The relevance of these findings to cryopreservation of spermatozoa is considered.