Fatty acid and energy (ATP-related compounds) metabolism of Eurasian perch (Perca fluviatilis) sperm: Endogenous metabolic strategy

Abstract

Structural (fatty acids) and energetic (ATP-related compounds) processes of spermatozoa of Eurasian perch (Perca fluviatilis) has been studied. Present study identified changes in fatty acids and adenosine phosphate stoichiometries as sperm ascended from basal metabolism (pre-activation quiescent state) to active metabolism (post-activation exhaustion). Results suggest long chain unsaturated (C14:0, C16:0) and monounsaturated fatty acids (C16:1) were significantly utilized (p < 0.05) for energy yielding purposes. Polyunsaturated fatty acids, C20:5n-3 (EPA) content was reduced from basal metabolism (1.09–2.57 mg g−1) to post-activation (0.69–2.39 mg g−1), while C20:4n-6 (ARA) and C22:6n-3 (DHA) remained preferentially conserved. In a way that ARA: EPA and DHA: EPA ratios became significantly higher (p < 0.05) in exhausted than quiescent state, for potential maintenance of membrane fluidity by DHA or eicosanoid activity (anti-inflammatory EPA to pro-inflammatory ARA balancing) during motility. Although endogenous fatty acid bioconversion capabilities could not be proved by the present study, these findings encourage future research. In terms of nucleotides, K-value (relative degradation of ATP; metabolic loss) was 30% at basal metabolism. ATP consumption equalled production at quiescent state, as the ratio of forward and backward reaction products in adenylate kinase reaction was maintained at ≈1 (equilibrium). With activation, 0.21–0.65 nmol ATP second−1 per 109 spermatozoa was metabolized and K-value showed 85–90% of pre-stored ATP pool degraded to non-calorific inosine and hypoxanthine. There was missing AMP, lowered ATP: ADP ratio and adenylate kinase reaction equilibrium was lost. We conclude a potential mismatch between glycolysis and substrates led to exhaustion in P. fluviatilis sperm, despite a tendency towards selective FA utilization to ensure membrane fluidity (DHA conservation) or prostaglandin and anti-inflammatory responses (ARA and EPA) till its last moments.