Effect of osmolality and oxygen tension on the survival of mouse sperm frozen to various temperatures in various concentrations of glycerol and raffinose
C. Koshimoto et al., Effect of osmolality and oxygen tension on the survival of mouse sperm frozen to various temperatures in various concentrations of glycerol and raffinose, CRYOBIOLOGY, 41(3), 2000, pp. 204-231
Cryopreserved mouse sperm are beginning to be used to meet the demand of a
reliable cost-effective method for maintaining the rapidly expanding number
s of lines of mutant mice. However, successful and reproducible cryopreserv
ation has proven to be a difficult problem. Furthermore, the underlying fac
tors responsible for success or failure are mostly obscure. Several contrib
utors to these difficulties have been identified. Our laboratory has found
that mouse sperm are extremely susceptible to the mechanical stresses assoc
iated with pipetting. mixing, and centrifugation, and others have found tha
t they are severely limited in their tolerance to osmotic volume changes. W
e have hypothesized two other contributors to the difficulties. One is that
the concentrations of glycerol used in published protocols are substantial
ly lower than those found to be optimal for most mammalian cells. The other
hypothesis relates to the fact that mouse sperm membranes are especially s
usceptible to damage from oxygen-derived free radicals. That damage may red
uce their ability to survive freezing. If so, survival ought to increase if
the concentration of oxygen is kept low throughout the procedure. To achie
ve low levels, we have incorporated an Escherichia coli membrane fraction,
Oxyrase, into all media. A previous report showed a protective effect. That
is confirmed here under a broader range of conditions. The conditions stud
ied have been the individual and interactive effects of the concentrations
of glycerol, raffinose, and phosphate-buffered saline (PBS) on motility aft
er freezing at 21 degreesC/min to -70 degreesC. Cryoprotection increased wi
th increasing raffinose concentration. provided that the concentration of P
BS was appropriately reduced to hold the total osmolality of nonpermeating
solutes to within tolerated limits. Surprisingly, the beat results were ach
ieved in the total absence of glycerol. The highest motilities to date (68
+/- 8%) after freezing to -70 degreesC have been achieved using media conta
ining Oxyrase, 0 M glycerol, and 18% raffinose in 1/4 x strength modified P
BS. We also determined the motility loss after freezing to intermediate tem
peratures, i.e., -10 and -30 degreesC. The major motility loss occurred by
- 10 degreesC, especially in the absence of Oxyrase. These results suggest
that a major problem in the freezing of mouse sperm is the physical stress
resulting from extracellular ice crystal formation. Oxyrase appears to less
en that damage substantially. (C) 2000 Academic Press.