Nongenomic Progesterone Receptors Mediated Bull Sperm Capacitation and Acrosome Reaction Are <scp>cAMP</scp>‐<scp>PKA</scp>‐Calcium Channel Dependent

Progesterone (P4) secreted from the cumulus cells mediates nongenomic signalling in sperm cells and induces capacitation and acrosome reaction in the oviduct. The induction of these events in bull spermatozoa is not fully understood. Recently, we reported the presence of membrane nongenomic P4 receptors in bull spermatozoa and the involvement of P4-nongenomic signalling through the involvement of complex signalling pathways with cannabinoid receptors in the regulation of bull sperm capacitation and acrosome reaction. Here in this study, using pharmacological agents, we report the involvement of cyclic adenosine 3'5' monophosphate-protein kinase A (cAMP-PKA) and calcium channels (sperm cation channel CatSper-and L-type) in the regulation of P4-dependent nongenomic induction of bull sperm capacitation and acrosome reaction. A total of 24 semen ejaculates were used in the study, and 1 picomolar (pM) and 1 micromolar (μM) P4 concentrations were used for capacitation and acrosome reaction induction, respectively in bull spermatozoa. Further, the P4-receptor blocker mifepristone (20 μM) and several other selective blockers KH7 (cAMP, 3 μM), P9115 (PKA, 10 μM), Nifedipine (L-type, 3 μM) and NNC 55-0396 (CatSper, 3 μM) were used for the exploration of downstream P4-signalling in the regulation of bull sperm capacitation and acrosome reaction. The sperm cells showed 50%-70% inhibition and reduction of P4-response in inducing capacitation and acrosome reaction after selective inhibition of these molecules during the study. Our results from the in vitro experiments in bull sperm cells suggested the involvement of cAMP-PKA, CatSper and L-type calcium channels during P4-induced bull sperm capacitation and acrosome reaction. These results also provided new insights into P4-nongenomic signalling in bull spermatozoa in the regulation of capacitation and acrosome reaction, further strengthening our understanding of these complex events in the oviduct.