Having ascertained using JC-1 as a probe that, in distinction with the controls, during capacitation boar sperm maintains high mitochondria] membrane potential (Delta Psi), to gain some insight into the role of mitochondria in capacitation, we monitored Delta Psi generation due to externally added metabolites either in hypotonically-treated spermatozoa (HTS) or in intact cells by using safranine O as a probe. During capacitation, the addition to HTS of L-lactate and succinate but not those of pyruvate, citrate and ascorbate + TMPD resulted in increase of Delta Psi generation. Accordingly, the addition of L-lactate and succinate, but not that of citrate, to intact sperm resulted in Delta Psi generation increased in capacitation. (C) 2015 Elsevier Inc. All rights reserved.