RELATIONSHIP BETWEEN SPERM ATP CONTENT AND MOTILITY OF CARP SPERMATOZOA

Carp spermatozoa are immotile in seminal plasma or in saline solution of high osmolality (>300 mosmol kg(-1)). These 'quiescent' spermatozoa initiate a progressive forward motility when transferred in freshwate r or in saline solution with low osmolality (<160 mosmol kg(-1)). In t his study we investigated 'in vitro' the relationship between sperm AT P content (measured by bioluminescence) and sperm motility (analysed b y videomicroscopy). Sperm ATP content remained high in the immobilizin g medium (200 mM KCl, Tris 30 mM, pH 8.0) where no flagellar movement occurs. Dilution of these spermatozoa in the activating medium (45 mM NaCl, 5 mM KCl, Tris 30 mM, pH 8.0) triggered forward motility which v aried with temperature. At 20 degrees C, sperm ATP content decreased r apidly during the progressive forward motility phase from 12 to 3 nmol /10(8) spermatozoa, concomitantly with decreases in velocity (130 to 1 0 mu m s(-1)) and the beat frequency (50 to 7 Hz). An inhibitor of mit ochondrial respiration (KCN 10 mM) produced a drop in sperm ATP conten t irrespective of the incubation medium (activating or immobilizing). A second phase of sperm motility in the activating medium was induced following a previous transfer of spermatozoa into a medium of high osm olality for a few minutes prior to the second phase. Within 10 minutes , spermatozoa recover 90% of the initial ATP level as well as forward motility. These results suggest that motility of carp spermatozoa depe nds on sperm ATP synthesized by mitochondrial respiration mainly store d before activation. In low osmolality conditions, the mitochondrial o xidative phosphorylation is unable to compensate for the ATP hydrolysi s required to sustain motility. The increase in osmolality surrounding spermatozoa probably blocks the dynein ATPases and allows an ATP 'reg eneration' as a result of mitochondrial respiration.