Combinations of fluorophore-loaded spermatozoa
assessed with SYBR-14/PI or Annexin-V/PI were used
to – indirectly – measure the proportions of spermatozoa
whose plasma membrane was absolutely stable
(PMS; using a marker for the phospholipid PS, such as
Annexin-V) or had started to undergo destabilization
(using the same marker) or erosion of the plasmalemma
(PMI; using PI and SYBR-14). Both PMS and PMI are
essential for cell viability and the ability of the
spermatozoon to interact with the environment, either
in the female genital tract during sperm transport or in
penetrating the oocyte vestments, including the zona
pellucida (ZP). Moreover, the plasma membrane is the
site where modifications occur during capacitation, the
acrosome reaction, and the events of ZP penetration and
fertilization [51]. Any modification of the stability or
intactness of the plasma membrane caused by handling,
including cryopreservation, would impair or at least
limit the fertilizing ability of the spermatozoa [21]. It is
probably for this reason that both PMI and PMS have
been reported to be more accurate in predicting fertility
than sperm Mot [52