DEGENERATION OF RESPIRATORY SYSTEM IN SEA-URCHIN SPERMATOZOA DURING INCUBATION IN SEAWATER FOR LONG-DURATION

Motility and respiration were examined in spermatozoa of the sea urchi n Hemicentrotus pulcherrimus after dilution and incubation in seawater at pH 8.2 at 20 degrees C. Almost all spermatozoa were motile during 12 hr of incubation, but their respiratory rate decreased gradually. T he acrosome reaction was also induced by egg jelly solution during 12 hr of incubation in seawater. However, the ratio of spontaneous acroso me reacted spermatozoa was quite low during the same period. An intrac ellular pH (pHi) of spermatozoa was about 7.5 just after dilution in s eawater and was almost constant during 12 hr of incubation. Upon dilut ion and incubation in seawater, activity of NADH-cytochrome c reductas e decreased in propotion to the decrease in the respiration in spermat ozoa, whereas cytochrome c oxidase activity was hardly changed. These suggest that the degeneration of respiratory system during 12 hr of in cubation in seawater is due to the decrease in the NADH-cytochrome c r eductase activity. In energy production system, phosphatidylcholine as a preferred substrate was efficiently hydrolyzed during 4 hr of incub ation and then the activity of the energy metabolism decreased gradual ly. Beyond 12 hr incubation in seawater, the number of immotile sperma tozoa increased and respiratory rate declined rapidly. Also, the perce ntage of the acrosome reaction induced by the egg jelly solution decre ased. These are probably due to the increase in the number of dead spe rmatozoa after 12 hr of incubation in seawater. It is thus concluded t hat the life-span of H. pulcherrimus spermatozoa is about 12 hr after dilution in seawater.