Energy metabolism of spermatozoa IV. Effect of calcium on respiration of mature epididymal sperm of the rabbit. Biol. Reprod

Epididymal sperm flushed from the caudae of mature rabbits with Tris-saline buffer containing EDTA are motile. The endogenous rate of respiration is stimulated by glucose or pyruvate. There is no further stimulation of the respiration rate by added Ca+2, and this rate is sensitive to inhibition by oligomycin which inhibits mitochondrial ATP synthesis and slows respiration, but which does not inhibit mitochondrial Ca+2 uptake with attendant increase in respiration rate. The sperm cell membrane is not permeable to Ca2, as shown by the observation that addition of the ionophore A23187, which makes cell membranes selectively permeable to Ca+2, results in a marked stimulation of respiration by added Ca+2. The stimulated rate is insensitive to inhibition by oligomycin, showing that the Ca+2 has direct access to the mitochondria which take up this cation in an energy-linked reaction. The presence of 45 mM l-1C03 in the medium stimulates the rate with pyruvate, but not with glucose, and does not affect the response to added Ca+2. Cyclic AMP and dibutyl cyclic AMP, with or without added Ca+2, also do not stimulate respiration with glucose or pyruvate as substrate. Mature rabbit sperm from the cauda epididymis are apparently intrinsically motile, needing only freedom from restraint and oxygen; a trigger in the form of Ca+2 is not needed