Heparin-induced capacitation but not intracellular alkalinization of bovine sperm is inhibited by Rp-adenosine-3',5'-cyclic monophosphorothioate

Abstract

The objective of this study was to investigate the importance of cAMP during capacitation of bovine sperm. The competitive antagonist of cAMP, Rp- adenosine-3'5'-cyclic monophosphorothioate (Rp-cAMP), blocked heparin- induced capacitation (p < 0.05). The effect of Rp-cAMP on heparin-induced capacitation was reversed by 8-bromo-cAMP. The maximal inhibitory effect on capacitation occurred when Rp-cAMP was added at the start of sperm incubation. These results support an important role for cAMP-dependent protein kinases during heparin-induced capacitation of bovine sperm. Further support for a role for protein phosphorylation during capacitation came from the use of the protein phosphatase inhibitor, okadaic acid. Okadaic acid had no affect on heparin-induced capacitation of bovine sperm (p > 0.05); however, bovine sperm were capacitated by okadaic acid in the absence of heparin (p < 0.05). The relationship of cAMP to capacitation-associated changes in sperm intracellular pH (pH(i)) was investigated using image analysis of bovine sperm. The pH(i) of sperm increased during capacitation, and Rp-cAMP did not affect the change in pH(i). We conclude that heparin- induced capacitation of bovine sperm involves an increase in cAMP and a protein phosphorylation event but that these do not induce the increase in pH(i) associated with capacitation.