Nucleotide content, oxydative phosphorylation, morphology, and fertilizingcapacity of turbot (Psetta maxima) spermatozoa during the motility period

The interdependence between motility, respiration, ATP production, and util ization was investigated in intact spermatozoa of turbot (Psetta maxima), a marine teleost. When spermatozoa were diluted in a hyperosmotic medium (>3 00 mOsmol/kg), they immediately became motile, and the intracellular concen tration of ATP as well as the adenylate energy charge ratio dropped concomi tant with the straight-line velocity. The ADP and AMP levels increased from 1.4 to 8.0 nmole/10(8) cells and from 0.6 to 6.0 nmole/10(8) cells, respec tively. Moreover, P-31-NMR spectra recorded prior to the swimming phase rev ealed the presence of phosphomonoesters (PMEs) and phosphodiesters (PDEs), intracellular inorganic phosphate (Pi), and phosphocreatine (PCr). At the e nd of the motility period, PCr, PDE, and PME decreased, while the Pi level increased markedly. Following initiation of motility, O-2 consumption of sp ermatozoa increased from 34.9 to 124.8 O-2 nmole/10(9) spermatozoa/min. FCC P, an uncoupler of oxydative phosphorylation, did not significantly affect the respiratory rate of motile spermatozoa. Ouabain, a specific inhibitor o f (Na+/K+)/ATPase, slightly decreased the respiration rate of motile sperma tozoa, indicating that the major part of ATP catabolism was linked to dynei n ATPase. Inhibitors of the respiratory chain (KCN, NaN3, NaHCO3-, oligomyc in) reduced sperm respiration, percentage of motile cells, velocity, and ad enylate contents. Following the reactivation of motility of demembranated s permatozoa, KCN, NaN3, NaHCO3- altered the flagellar beat frequency, demons trating that these respiratory inhibitors possess action sites other than m itochondria, Mitochondrial oxydative phosphorylation is highly requested to produce energy required during motion. Nevertheless it is insufficient to maintain endogenous ATP stores. A second phase of motility was induced by a transfer of exhausted spermatozoa into an ionic medium of low osmolality ( 200 mOsmol/kg) for 30 min. Spermatozoa, once reactivated in AM, recovered 5 5% of initial motility and 31% of initial fertilization rate. In hypo-osmot ic medium, mitochondrial oxydative phosphorylation also induced ATP regener ation. Following activation of movement, several morphological changes were observed in the mitochondria and the midpiece. Mel. Reprod. Dev. 53:230-24 3, 1999, (C) 1999 Wiley-Liss, Inc.