Stallion spermatozoa surviving freezing and thawing experience membrane depolarization and increased intracellular Na+

In order to gain insight of the modifications that freezing and thawing cause to the surviving population of spermatozoa, changes in the potential of the plasma membrane (Em) and intracellular Na+ content of stallion spermatozoa were investigated using flow cytometry. Moreover, caspase 3 activity was also investigated and the functionality of the Na+-K+ ATPase pump was investigated before and after freezing and thawing. Cryopreservation caused a significant (pamp;lt;0.001) increase in the subpopulation of spermatozoa with depolarized sperm membranes, concomitantly with an increase (pamp;lt;0.05) in intracellular Na+. These changes occurred in relation to activation of caspase 3 (pamp;lt;0.001). Cryopreservation reduced the activity of the Na-K+ pump and inhibition of the Na+-K+ ATPase pump with ouabain-induced caspase 3 activation. It is concluded that inactivation of Na+-K+ ATPase occurs during cryopreservation, an inhibition that could play a role explaining the accelerated senescence of the surviving population of spermatozoa.
Funding Agencies|Ministerio de Economia y Competitividad-FEDER, Madrid, Spain [AGL2013-43211-R]; Junta de Extremadura-FEDER [GR 15029, IB16030]; Swedish Research Councils VR [521-2011-6353]; Formas [221-2011-512]; Ministerio de Educacion, Cultura y Deporte, Madrid Spain [FPU13/03991]; Ministerio de Economia y Competitividad Juan de la Cierva [IJCI-2014-21671]