Polymyxin B enhances acrosomal exocytosis triggered by calcium and the calcium ionophore A23187 in ejaculated boar spermatozoa

Polymyxin B (PMB) is beneficial for boar semen storage since it neutralizes the endotoxin of bacteria. However, the direct effect of PMB on boar spermatozoa has been unknown. This study aimed to examine the effect of PMB on acrosomal exocytosis, an essential process for successful fertilization in boar spermatozoa. Ejaculated spermatozoa stored with BTS extender at 17°C were washed and incubated with 0–100 μM PMB for 20 min and then examined for % total motililty, vigor grade and viability. None of the parameters was significantly different between 0 and 50 μM PMB with a gradual decline at higher concentrations. Thus the effect on acrosomal exocytosis was investigated at 0–50 μM of PMB. Spermatozoa were preincubated with PMB for 10 min, incubated for stimulation of acrosomal exocytosis with Ca(2+) and the calcium ionophore A23187 and then fixed with glutaraldehyde at 5, 10 and 15 min. Preincubation with PMB at 0.01–50 μM and 0.05–50 μM resulted in significant enhancement of acrosomal exocytosis at 10 min and 15 min of incubation, respectively. Preincubation with PMB followed by incubation without A23187 did not affect acrosomal exocytosis. These results suggest that PMB exerts effects on the acrosomal exocytosis triggered by Ca(2+) and A23187 in boar spermatozoa.