Factors stabilizing bull sperm cell volume and prolonging motility at high dilution

Sperm cell volume changes were monitored electronically, and motility was observed microscopically during incubation at 35 °C in chemically defined media isosmotic with 0.15 M NaCl and buffered at pH 7.0. Neither 2.0 mM Pi nor 10 mM Mg²⁺ had any marked effects on cell volume stability or motility when used with different levels of fructose and K⁺. Both 3.0 mM K⁺ and 10 mM fructose significantly (P < 0.05) delayed the onset of cellular swelling, but this delay and the effects on motility were minimal in overcoming the ‘dilution effect’. EDTA (0.05–1.0 mM) had a marked stabilizing effect on cell volume and essentially doubled the duration of motility. When EDTA was combined with fructose the effects were more beneficial than with either one alone. BSA (1 mg/ml) also stabilized cell volume in the presence and absence of fructose, and markedly prolonged vigorous sperm motility. BSA and EDTA tended to be additive in effect.CN⁻markedly improved the otherwise limited beneficial effects of fructose on sperm volume stability and motility even in the presence of oligomycin. Without fructose, CN⁻ caused early swelling and an apparent eventual cell lysis. CN⁻ could not abolish the beneficial effects of BSA in the presence of fructose or those of BSA or EDTA during preincubation without fructose.Oligomycin blocked the beneficial response to EDTA or BSA in the absence of fructose, but it did not prevent the improvement and extension of motility caused by EDTA, BSA or CN⁻ when fructose was included. Oligomycin caused immediate swelling followed by cell shrinkage to less than the initial cell volume. The onset of shrinkage could be delayed by fructose and further delayed if CN⁻, EDTA or BSA was also included. The delay in onset of shrinkage was accompanied by prolonged motility.Spermatozoa, immobilized by preincubation in a fructose-free media containing CN⁻, could be activated by the addition of fructose up to the time swelling began. Both BSA and EDTA extended this period during which motility could be restored.