The Physiology of Sea-Urchin Spermatozoa

Abstract

1. An investigation has been made into the causes of the interrelated phenomena of Senescence and the Dilution Effect in the spermatozoa of Echinus esculentus. The Dilution Effect is the increase in O₂ uptake and in movement observed when a concentrated sperm suspension, obtained by partial dilution of semen, is diluted with sea water. 2. The supernatant sea water obtained by centrifuging partially metabolized sperm suspensions contains no substances which depress the respiration or motility of the spermatozoa of the same species. This supernatant sea water has a small but definite protective action on spermatozoa in maintaining but not increasing their O₂ consumption. The effect is enhanced by agitating the suspensions before centrifugation. 3. E. esculentus spermatozoa do not glycolyse aerobically, anaerobically, or in the presence of 5% O₂ in CO. The absence of aerobic acid production proves that the reduced O₂ uptake per sperm of dense suspensions is not due to a lowering of the pH of the medium. 4. As the Dilution Effect is observed in manometric experiments in which CO₂ is continuously and adequately removed, neither accumulation of CO₂ nor a reduction in pH resulting from the accumulation of CO₂ are responsible for the reduced O₂ uptake of dense suspensions. 5. The O₂ uptake of dense sperm suspensions (> 10⁹ sperm/ml.) is altered by changes in O₂ tension. O₂ consumption in 100% oxygen is nearly double that in 10% O₂ in N₂. An increase in O₂ tension has no stimulating action on dilute suspensions. 6. An atmosphere of 100% O₂ has a gradual toxic effect on dense and dilute sperm suspensions. 7. Carbon monoxide has a greater inhibitory action on dilute than on concentrated sperm suspensions. 8. The difference between the effects of varying O₂ tensions or CO on dense and dilute suspensions is partly, or perhaps wholly, due to gaseous diffusion being a limiting factor. This may partly explain the Dilution Effect. 9. Apart from photo-reversibly inhibiting respiration, CO exerts an irreversible toxic influence on sea-urchin spermatozoa. 10. Illumination of spermatozoa with a wave-length of light outside the region of photo-chemical absorption by CO cytochrome oxidase enables visual examination to be made in the presence of CO. The O₂ uptake of a suitable concentration of spermatozoa is 70% inhibited by 5% O₂ in CO. The same inhibition occurs when the suspension is illuminated by light of wave-length 548 mµ, but there is no equivalent decrease in motility. 11. After motility and respiration have ceased sea-urchin spermatozoa still contain oxidizable substrates and the appropriate dehydrogenases as evidenced by their ability to reduce methylene blue in an evacuated Thunberg tube.