Maintenance of steelhead trout (Oncorhynchus mykiss) sperm at different in vitro oxygen tensions alters ATP levels and cell functional characteristics

Adenosine triphosphate (ATP) levels in sperm from steelhead trout (Oncorhynchus mykiss) were found to be 12.0 ± 1.4 pmol ATP per 10⁶ sperm cells. Sperm were stored at 0–2 °C for up to 72 h under 100 and 21% O₂, and 100% N₂. The sperm ATP content of samples maintained under 100 and 21% O₂ both decreased to about 70 and 50% of initial values after 24 and 72 h, respectively. ATP levels of sperm stored under 100% N₂ decreased to 20% of initial values after only 4 h and to less than 10% of initial values after 24 h; they remained unchanged throughout the following 48 h. These low levels, however, were reversible. Following 4 h incubation under 100% N₂, sperm ATP levels rose upon exposure to and maintenance under 100% O₂, increasing to 50% of initial values after a total of 72 h. ATP levels in sperm maintained with cyanide for 4 h decreased to less than 5% of initial values. The magnitude of the change in sperm ATP levels after 24 h in samples maintained under 100% O₂ correlated positively with the initial sperm ATP levels. Sperm ATP levels, motility, and fertility were all correlated positively in a subset of samples examined. The initial percent of living sperm (sperm viability) was 97.5 ± 0.5% and was unaltered through 24 h under all O₂ tensions. Sperm viability remained unchanged through 72 h under 21% O₂ and decreased by 10 and 30% by 72 h under 100% O₂ and 100% N₂, respectively. Therefore, reductions in sperm ATP levels could not be attributed to cell death as viability decreased only modestly over these durations. Spermatocrit values were unaltered throughout the 72 h incubation for samples maintained under 100 and 21% O₂, however, a 95% increase in spermatocrit occurred after 72 h in samples maintained under 100% N₂. These data indicate that intracellular ATP in steelhead trout sperm can be modulated by ambient oxygen without significant loss of viability and that this ATP has a probable role in cell motility and fertility, and sperm packing and cell flexibility.