DETERMINATION OF WATER PERMEABILITY COEFFICIENT AND ITS ACTIVATION-ENERGY FOR RABBIT SPERMATOZOA

Critical tonicity (tonicity at which 50% of cells swell beyond their m aximum volume-to-surface area ratio and lyse) of rabbit spermatozoa wa s measured as 45.6 mOsm at 22 degrees C. To determine the temperature effect on critical tonicity, cells were equilibrated to 15, 25, and 35 degrees C and critical tonicity was measured as 52.9, 42.2, and 32.4 mOsm, respectively. The time taken for rabbit sperm to achieve lysis a t these temperatures was measured by exposing cells for increasing tim es to distilled water. From these results values for the permeability coefficient of rabbit spermatozoa to water (L(p)) and its activation e nergy (E(a)) were calculated. At 25 degrees C, L(p) was 0.63 mu m/min/ atm and was clearly temperature dependent; E(a) was 17.8 kcal/mol. Rab bit spermatozoa appear to have a low L(p) and high E(a), the opposite of the situation seen with spermatozoa from all other species examined to date which have high L(p) and low E(a). Nevertheless, the values o btained permit modeling of cooling rates for cell survival during cryo preservation in keeping with cooling rates commonly employed. (C) 1995 Academic Press, Inc.