Lactate dehydrogenase in fish spermatozoa and its role in sperm cell bioenergetics

Abstract

Lactate dehydrogenase (LDH) in spermatozoa of three fish species was studied to determine its role in sperm cell bioenergetics in normal and polluted conditions. The adenylate energy charge (AEC) has been used as the measure of energy storage for adenine nucleotide pool of living cells and tributyltin (TBT) as a model toxicant. It was demonstrated that carp Cyprinus carpio Linnaeus, 1758 spermatozoa exhibit higher LDH activity than catfish Clarias gariepinus (Burchell, 1822) and herring Clupea harengus Linnaeus, 1758 spermatozoa. Native electrophoretic pattern of LDH from spermatozoa compared to somatic tissues extract shows nine LDH isoenzymes in carp spermatozoa, two LDH isoenzymes in herring and one LDH isoenzyme in catfish spermatozoa. It was confirmed that lactate plus pyruvate, which are the substrates for LDH seems to maintain AEC value. It indicates ATP synthesis in tricarboxylic acid cycle prevails upon the ATP utilization in catfish spermatozoa. It was noticed that LDH-B4 is more strongly inhibited by TBT in herring than the nine LDH isoenzymes in carp spermatozoa which confirms that herring spermatozoa may be more sensitive for pollution by decreasing their energetic state. LDH role in maintaining physiological bioenergetic state of spermatozoa is also discussed.