Lactate dehydrogenase-C4 is involved in heparin- and NADH-dependent bovine sperm capacitation

Lactate dehydrogenase C4 isoenzyme (LDH-C4) is involved in the energy metabolism of spermatozoa. Sperm capacitation is considered part of an oxidative process; an NADH oxidase of plasma membrane could be responsible for superoxide anion generation which is required for capacitation. The role of LDH-C4 and the requirements of NADH in cryopreserved bovine sperm capacitation were studied. LDH-C4 activity was 5.52 +/- 3.41, 15.72 +/- 6.04 and 15.22 +/- 1.92 Units 1010 spermatozoa-1 in plasma membrane, sperm suspension and cytosol fraction, respectively; these activities were inhibited by sodium oxamate. To study the influence of oxidative substrates in capacitation, three different TALP (T) media were used: TP (pyruvate); TL (lactate) and TC (citrate); heparin or NADH was then added. There were no significant differences in the percentage of capacitation induced by heparin or NADH in TALP medium; similar levels of capacitation were achieved with TL alone or TL +heparin and TP +NADH; capacitation was inhibited with sodium oxamate in all treatments used. Cytosolic NADH may be required as a substrate for sperm oxidase. Lactate influx through plasma membrane may be utilized by cytosolic LDH-C4, increasing reduced coenzymes required for capacitation. Plasma membrane LDH-C4 may participate in the production of lactate to obtain intracellular reducing equivalents to be used by sperm oxidase for in vitro sperm capacitation.