Elucidation of the mechanism responsible for the temperature-dependent reversible inactivation of the motility of fowl spermatozoa.

1. When washed fowl spermatozoa were held at 30 degrees C in a Ca++-free medium they retained internal Ca++, assimilated from the seminal plasma in vivo, which maintained their motility. 2. When this preparation was warmed to 40 degrees C, Ca++ was lost to the medium and the spermatozoa became immotile. 3. On subsequent cooling to 30 degrees C, the spermatozoa were capable of re-sequestering the Ca++, which restored their motility. 4. Removal of internal Ca++, with subsequent reduction of cellular activity, improved the survival of fowl spermatozoa held at 30 degrees C.