Role of the Calcium-Sensing Receptor (CaSR) in bovine gametes and during in vitro fertilization.

Calcium Sensing Receptor (CaSR) is a G-protein coupled receptor which senses extracellular calcium and activates diverse intracellular pathways. The objective of our work was to demonstrate the presence of CaSR in bovine gametes and its possible role in fertilization and embryo development. The location of CaSR was demonstrated by immunofluorescence in bovine gametes; additionally bovine sperm were incubated with 5, 10 and 15 μM of the specific CaSR inhibitor NPS2143 in a Tyrode's Albumin Lactate Pyruvate medium (4 h). Sperm viability was maintained for all concentrations tested while total motility decreased significantly at 10 and 15 μM. Addition of 15 μM of NPS2143 during oocyte in vitro maturation did not alter the maturation rate. When NPS2143 (15 μM) was added to the fertilization medium during sperm-oocyte co-incubation the cleavage, morula and blastocyst rates remained unchanged. To confirm if 15 μM of NPS2143 exerted any effect on embryo development, NPS2143 was added to the embryo culture medium. Cleavage rates remained unchanged when 15 μM of NPS2143 was added to the culture medium (79.1 ± 6.8 vs. 73.7 ± 5.3; mean % ± SEM; p > 0.05, control vs. inhibitor). By contrast, development to the morula (46.6 ± 7.3 vs. 24.3 ± 4.3; mean % ± SEM; p < 0.05) and blastocyst stages (29.9 ± 9.0 vs. 9.9 ± 3.6; mean % ± SEM; p < 0.05) decreased (control vs. inhibitor). Our results demonstrate a key role of CaSR on sperm motility and embryo development but not on oocyte maturation or fertilization in the bovine species.