Human Reproduction, Vol. 14, No. 7, 1827-1832,
July 1999
© 1999 European Society of Human Reproduction and Embryology
Lipid dynamics in the plasma membrane of fresh and cryopreserved human spermatozoa
1 Department of Signalling, The Babraham Institute, Cambridge CB2 4AT, 2 Department of Food Biophysics, Institute of Food Research, Norwich NR4 7UA and 3 Department of Obstetrics & Gynaecology, Rosie Maternity Hospital, University of Cambridge, Cambridge CB2 2SW, UK
Preserving the integrity of the plasma membrane of spermatozoa is crucial for retention of their fertilizing capacity, especially after stressful procedures such as freezing and storage. In this investigation we have measured lipid diffusion in different regions of the plasma membrane of fresh and cryopreserved human spermatozoa using a sensitive, high resolution fluorescence photobleaching technique (FRAP) with 5-(N-octadecanyl)aminofluorescein as reporter probe. Results show that diffusion was significantly faster on the plasma membrane overlying the acrosome and decreased progressively in the postacrosome, midpiece and principal piece. The midpiece plasma contains a higher proportion of immobile lipids than other regions. In cryopreserved spermatozoa, lipid diffusion in the plasma membrane was significantly reduced on the acrosome, postacrosome and midpiece relative to fresh spermatozoa. Diffusion, however, could be restored to normal levels by washing spermatozoa in a medium containing 0.4% polyvinylpyrrolidine but not in medium alone or in medium containing 0.4% albumin. These results suggest that (i) lipid dynamics in the plasma membrane of human spermatozoa varies significantly between surface regions; (ii) in-plane diffusion is adversely affected by cryopreservation; and (iii) washing frozen spermatozoa in 0.4% polyvinylpyrrolidine restores membrane lipid fluidity to normal levels. The latter finding has important implications for improving the fertility of human spermatozoa following cryopreservation.
Key words: cryodamage/diffusibility/membrane lipid domains/photobleaching
4 To whom correspondence should be addressed at: Gamete Signalling Laboratory, The Babraham Institute, Cambridge CB2 4AT, UK. E-mail: roy.jones{at}bbsrc.ac.uk
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