The role of bicarbonate in the modulation of capacitation, spontaneous acrosome reaction and motility of equine fresh and frozen spermatozoa

In this study, we defined the composition of the culture medium that yield a significant percentage of alive and functional equine spermatozoa during enough time before artificial insemination. The effects of sodium bicarbonate were analyzed in fresh and frozen semen in respect to sperm viability, capacitation, spontaneous acrosome reaction and several kinetic parameters such as total motility, progressive motility, VCL, VSL, ALH, BCF, LIN. Moreover, employing Bayk-6844 and Nifedipine, the involvement of L- type voltage-gated calcium channels in the modulation of intracellular calcium concentrations was investigated. Results evidenced an immediate effect of sodium bicarbonate in reducing fresh sperm viability and in increasing capacitation and spontaneous acrosome reaction of fresh and frozen sper- matozoa. Furthermore, it affected total and progressive motility of fresh and frozen semen. Because of the sudden effects of the compound, we think that a buffer lacking sodium bicarbonate is more suitable to preserve the viability and the functional state of equine spermatozoa required to undergo at the right time those modifications necessary for fertilization. We also demonstrated that intracellular calcium modifications induced by Bayk-8644 and Nifedipine are not involved in signals related to vitality, capacitation, spontaneous acrosome reaction and motility.