Treatment of cryopreserved bovine sperm with calcium ionophore A23187 increases in vitro embryo production

Abstract

After ejaculation, mammalian sperm undergo a series of molecular events conducive to the acquisition of fertilizingcompetence. These events are collectively known as capacitation and involve acrosomal responsiveness and avigorous sperm motility called hyperactivation. When mimicked in the laboratory, capacitating bovine spermmedium contains bicarbonate, calcium, albumin and heparin, among other components. In this study, we aimedat establishing a new capacitation protocol for bovine sperm, using calcium ionophore. Similar to our findings usingmouse sperm, bovine sperm treated with Ca2+ ionophore A23187 were quickly immobilized. However, thesesperm initiated capacitation after ionophore removal in fresh medium without heparin, and independent of theProtein Kinase A. When A23187-treated sperm were used on in vitro fertilization (IVF) procedures without heparin,eggs showed cleavage rates similar to standardized IVF protocols using heparin containg synthetic oviductfluid (IVF-SOF). However, when A23187 pre-treated sperm were further used for inseminating eggs in completeIVF-SOF-heparin, a significantly higher percentage of embryo development was observed, suggesting a synergismbetween two different signaling pathways during bovine sperm capacitation. These results have the potentialto improve current protocols for bovine IVF that could also be applied in other species of commercial interest.