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The tonicity of murine epididymal spermatozoa and their permeability towards common cryoprotectants and epididymal osmolytes

¹ Institute of Reproductive Medicine of the University, Domagkstrasse 11, D-48129 Münster, Germany² Department of Biological Sciences, University of New Orleans, New Orleans, Louisiana, USA

Correspondence should be addressed to T G Cooper; Email: trevorg.cooper{at}ukmuenster.de

The permeability of murine cauda epididymidal spermatozoa was determined from the swelling caused by penetrating agents at isotonicity, which lies between 422 and 530 mmol/kg. Spermatozoa were permeable to a range of solutes with size <200 Da. Relative entry rates of cryoprotective agents (CPAs) were ethylene glycolDMSO>propane-1,2-diol>glycerol>propane-1,3-diol. More polar compounds including major epididymal secretions were impermeant. None of the compounds entered spermatozoa through quinine-sensitive channels; rather, quinine increased the size of solute-swollen spermatozoa, suggesting that regulatory volume decrease and osmolyte loss occurred under these conditions. Volume responses to lowered osmolality revealed a greater volume-regulating ability of spermatozoa from the B6D2F1 strain than the C57BL6 strain. As the former strain displays better post-thaw fertility, their spermatozoa may have greater osmolyte loads enabling them to cope better with osmotic stress. Inadequate volume regulation, due to CPA-induced osmolyte loss, may affect post-thaw fertility. Knowing the permeability towards cryoprotectants will help to make a better choice of CPAs that are less damaging to sperm during cryopreservation.