Effects of osmolality, morphology perturbations and intracellular nucleotide content during the movement of sea bass (Dicentrarchus labrax) spermatozoa

Sea bass spermatozoa are maintained immotile in the seminal fluid, but init iate swimming for 45 s at 20 degrees C, immediately after dispersion in a h yperosmotic medium (1100 mOsm kg(-1)). The duration of this motile period c ould be extended by a reduction of the amplitude of the hyperosmotic shock. Five seconds after the initiation of motility, 94.4 +/- 1.8% of spermatozo a were motile with a swimming velocity of 141.8 +/- 1.2 mu m s(-1), a flage llar beat frequency of 60 Hz and a symmetric type of flagellar swimming, re sulting in linear tracks. Velocity, flagellar beat frequency, percentage of motile cells and trajectory diameter decreased concomitantly throughout th e swimming phase. After 30 s of motility, the flagellar beat became asymmet ric, leading to circular trajectories. Ca2+ modulated the swimming pattern of demembranated spermatozoa, suggesting that the asymmetric waves produced by intact spermatozoa after 30 s of motility were induced by an accumulati on of intracellular Ca2+. Moreover, increased ionic strength in the reactiv ation medium induced a dampening of waves in the distal portion of the flag ellum and, at high values, resulted in an arrest of wave generation in deme mbranated spermatozoa. In non-demembranated cells, the intracellular ATP co ncentration fell immediately after transfer to sea water, in contrast, the AMP content increased during the same period, while the ADP content increas ed slightly. in addition, several morphological changes affected the mitoch ondria, chromatin and midpiece. These results indicate that the short swimm ing period of sea bass spermatozoa is controlled by energetic and cytoplasm ic ionic conditions and that it is limited by osmotic stress, which induces marked changes in cell morphology.