Effects of bovine serum albumin (BSA) and bicarbonate on the achievement of in vitro capacitation and subsequent progesterone-induced acrosome reaction in boar spermatozoa

Abstract

The objective of the present work was to evaluate the effects of different concentrations of bicarbonate and bovine serum albumin (BSA), added to the in vitro capacitation medium, on the induction of the acrosome reaction in boar semen. Eight different treatments with different concentrations of bicarbonate (0, 5, 15 and 38 mM) and BSA (0 and 5 mg / ml) were tested: 1) negative control (No BSA / No Bic), which was the basic medium without bicarbonate or BSA; 2) basic medium supplemented with 5 mg/mL BSA only (BSA / No Bic); 3) basic medium supplemented with 5 mM NaHCO3 and 5 mg/mL BSA (BSA + 5 mM Bic); 4) basic medium supplemented with 5 mM NaHCO3 only (No BSA + 5 mM Bic); 5) basic medium supplemented with 5 mM NaHCO3 and 5 mg/mL BSA (BSA + 15 mM Bic); 6) basic medium supplemented with 15 mM NaHCO3 only (No BSA + 15 mM Bic); 7) basic medium supplemented with 38 mM NaHCO3 and 5 mg/mL BSA (BSA + 38 mM Bic); and 8) basic medium supplemented with 38 mM NaHCO3 only (No BSA + 38 mM Bic). Sperm cells were submitted to the medium and incubated at 38.5 oC with 5% of CO2 for 5 h. Sperm motility, membrane integrity, membrane lipid disorder, intracellular calcium levels, mitochondrial activity and tyrosine phosphorylation levels of GSK3α and DARPP32 were determined after 0, 2 and 4 h of incubation and after 30 and 60 min of the addition of progesterone. The medium without BSA did not capacitated, generating similar results to the non-capacitive medium (without BSA and without bicarbonate) (P <0.05). Mediums with BSA and bicarbonate at 15 or 38 mM showed high (P <0.05) levels of calcium (Fluo-3 and Rhod 5), lipid disorder (M540) and protein phosphorylation (GSK3α). The medium with BSA and 15 mM bicarbonate presented (P <0.05) greater motility and viability than the medium with BSA and bicarbonate at 38 mM. The medium with BSA and without bicarbonate or with 5 mM bicarbonate, were capacitated, however with lower indices than medium containing BSA and bicarbonate at 15 or 38 mM. The analyzes showed that the in vitro capacitation of boar semen is related to the presence of BSA in the capacitive medium and the presence of bicarbonate is not a limiting factor for the capacitation. The medium that obtained the best qualification result was BSA with bicarbonate at 15 mM.