Mouse sperm displays a CatSper-independent rapid increase in intracellular calcium during capacitation

SCHIAVI-EHRENHAUS LJ; ROMAROWSKI A; BUFFONE MG; MARTÍN-HIDALGO D; VISCONTI PE; LUQUE GM; KRAPF D

Mar del Plata

Congreso; Reunión Anual de Sociedades de Biociencia. SAIC, SAFE, SAB, SAP, AACYTAL.; 2019

Freshly ejaculated mammalian sperm do not have the ability to fertilize oocytes. They must undergo a functionally defined process called capacitation, which allows them to develop hyperactivated motility and the ability to undergo acrosomal exocytosis. Sperm become capacitated in vivo by interacting with the female reproductive tract or in vitro in a defined capacitation medium that contains bovine serum albumin (BSA), calcium (Ca2+), and bicarbonate (HCO3-;). We previously have shown that only a subpopulation of live sperm respond to incubation in capacitating medium by increasing the intracellular Ca2+ concentration ([Ca2+]i). This increase became rapidly evident, within one minute of incubation, and it remained sustained for the 90 minutes of capacitation. In this work, flow cytometry was used to analyse early changes in [Ca2+]i during capacitation. For this purpose, sperm were double stained with the Ca2+ dye Fluo-4 AM in combination with propidium iodine to analyze these changes in individual live sperm. We observed that the early increase in [Ca2+]i was dependent on the presence of extracellular Ca2+. In addition, it was determined that, unlike the late capacitation-associated [Ca2+]i increase, the early rise was independent of CatSper channels, as sperm derived from CatSper knockout (CatSper KO) or incubated in the presence of CatSper inhibitors showed a significant increase in [Ca2+]i. In accordance to these findings, inhibition of sAC/PKA pathway didn?t affect this early increase. Our results suggest that Ca2+ may be entering into the cell trough a Ca2+ channel and not a pump, as sperm incubated in the presence of Ni2+ failed to increase [Ca2+]i. We also determined that this rise is mainly promoted by the presence of BSA in the capacitation media. Taken together, our results indicate that there is a rapid entry of Ca2+ into a subpopulation of capacitated sperm, through a Ca2+ channel sensitive to BSA but not HCO3-, and independent of the sAC/PKA pathway.