HEPARIN-INDUCED CAPACITATION BUT NOT INTRACELLULAR ALKALINIZATION OF BOVINE SPERM IS INHIBITED BY RP-ADENOSINE-3',5'-CYCLIC MONOPHOSPHOROTHIOATE

The objective of this study was to investigate the importance of cAMP during capacitation of bovine sperm. The competitive antagonist of cAM P, Rp-adenosine-3'5'-cyclic monophosphorothioate (Rp-cAMP), blocked he parin-induced capacitation (p < 0.05). The effect of Rp-cAMP on hepari n-induced capacitation was reversed by 8-bromo-cAMP. The maximal inhib itory effect on capacitation occurred when Rp-cAMP was added at the st art of sperm incubation. These results support an important role for c AMP-dependent protein kinases during heparin-induced capacitation of b ovine sperm. Further support for a role for protein phosphorylation du ring capacitation came from the use of the protein phosphatase inhibit or, okadaic acid. Okadaic acid had no affect on heparin-induced capaci tation of bovine sperm (p> 0.05); however, bovine sperm were capacitat ed by okadaic acid in the absence of heparin (p < 0.05). The relations hip 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 affec t the change in pH(i). We conclude that heparin-induced capacitation o f bovine sperm involves an increase in cAMP and a protein phosphorylat ion event but that these do not induce the increase in pH(i) associate d with capacitation.