Association of lactate, intracellular pH, and intracellular calcium during capacitation and acrosome reaction: contribution of hamster sperm dihydrolipoamide dehydrogenase, the E3 subunit of pyruvate dehydrogenase complex.

The role of dihydrolipoamide dehydrogenase (DLD), the E3 subunit of the pyruvate dehydrogenase complex (PDHc) in hamster sperm capacitation and acrosome reaction has been implicated previously. In this study, attempt has been made to understand DLD/PDHc involvement from the perspective of pyruvate/lactate metabolism. Inhibition of DLD was achieved by the use of a specific inhibitor, 5-methoxyindole-2-carboxylic acid. It was seen that 5-methoxyindole-2-carboxylic acid-treated spermatozoa with inhibited DLD (and PDHc) activity had lactate accumulation, which caused an initial lowering of the intracellular pH and calcium and an eventual block in capacitation and acrosome reaction. Collectively, the data reveal a significant contribution of the metabolic enzymes DLD and PDHc to lactate regulation in hamster spermatozoa during capacitation and acrosome reaction. Additionally, the importance of lactate regulation in the maintenance of sperm intracellular pH and calcium, two important physiologic factors essential for sperm capacitation and acrosome reaction, has also been established.