Deduction of a calcium ion circuit affecting rooster sperm in vitro.

Four premises for rooster sperm preservation were outlined previously. Understanding mitochondrial Ca cycling in terms of whole-cell Ca flux was one premise. The present work tested the hypothesis that sperm mitochondria can be damaged by intracellular as well as extracellular Ca. Sperm were washed by centrifugation through 12% (wt/vol) Sperm were washed by centrifugation through 12%(at/vol) Accudenz to procure sperm at a physiological concentration within a chemically-defined suspension. Five solutions were tested. Each solution contained 30 m glucose, and had an osmolality of 320 mmol/kg and a pH of 7.4. Washed sperm were diluted to 2.0 × 10 sperm/mL. Each replicate sperm suspension was cooled to 10°C. Sperm mobility was measured after 1, 2, 4, 8, 12, and 24 h. Data were plotted as a function of time in each experiment. Function type was confirmed by lack of fit analysis. A parabola with a maximum at 3.7 h was observed when sperm were suspended in 205 m taurine buffered with 50 m-tris[hydroxyl-methyl]methyl-2-amino-ethanesulfonic acid (TES). This effect was attributed to a Ca flux from the nuclear envelope into mitochondria. An exponential decay was observed when TES-buffered taurine contained 2 m Ca. This effect was attributed to mitochondrial Ca overload induced by uptake of extracellular Ca. Exponential decay also was observed when TES-buffered taurine contained a Ca chelator. This effect was attributed to a Ca flux from the nuclear envelope through mitochondria and then into an extracellular Ca sink. This possibility was supported by the response of sperm to thapsigargin. Specifically, inhibition of sarcoendoplasmic reticulum Ca-ATPase compromised sperm mobility relative to a buffer control. Finally, a 60 m phosphate buffer containing 2 m citrate yielded a linear relationship in contrast to the TES-buffered solutions tested. Sperm mobility after 24 h of storage in the phosphate buffer was 92% of that observed for prewashed sperm. The linear response was attributed to weak chelators providing resistance within a Ca circuit and thereby preventing mitochondrial Ca overload. Fertility, however, was compromised when hens were inseminated with mobile sperm recovered after either 8 or 24 h of storage at 10°C. In conclusion, sperm cell Ca homeostasis was proven to be critical for maintaining sperm mobility in vitro, but mitochondrial Ca uptake is not the sole phenomenon that compromises sperm function during in vitro storage.