Calcium transport in diluted or cooled ram semen

Ram semen was subjected to various dilution rates and temperatures of dilution, and was also subjected to slow cooling and rewarming. Calcium ion movements across sperm membranes were measured using the radioisotope 45Ca2+. It was shown that even 2- to 4-fold dilution caused an increase in intracellular calcium content. An increase in intracellular calcium also occurred in proportion to a decreased temperature of dilution. After an initial increase in intracellular calcium content, spermatozoa appeared able to restore a low intracellular calcium level over a period of 2 h at 22 degrees C or above. This ability was lost at 16 degrees C or below. However, if undiluted semen was slowly cooled (0.125 degrees C/min) even to 5 degrees C and rewarmed to 22 degrees C before dilution, the spermatozoa regained this ability. In contrast, spermatozoa rapidly cooled to 5 degrees C and rewarmed to 22 degrees C before dilution were not able to restore the low intracellular calcium level.