The Physiology of Sea-Urchin Spermatozoa

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Abstract
1. Sea-urchin spermatozoa (Echinus esculentus) are extremely sensitive to changes in the pH of the suspending medium, their respiration being proportional to pH between 7.6 and 8.4. 2. In a manometric experiment in which semen was diluted 1/25 with sea water (CO2 absorbed), the pH of the suspension was 7.5 at the beginning of the experiment and 8.2 at the end, after 180 min. incubation at 15° C. 3. Sea water, buffered with glycyl glycine, 0.025 M and brought to pH 8.3, was added to a sperm suspension whose pH was 7.5 at the beginning of the experiment, after a period of incubation. There was a pronounced respiratory Dilution Effect. When the sea water was buffered with glycyl glycine and brought to pH 7.8, and this diluent was added to the same sperm suspension, there was a negligible respiratory Dilution Effect. 4. The O2 uptake of suspensions prepared in buffered sea water at pH 8.3 was markedly higher than that in the same buffered sea water at pH 8.0. 5. These observations cast doubt on the reality of the respiratory Dilution Effect when observed in experiments in which sea water is the suspending medium and respiration is measured by a method involving the absorption of CO2. An exception to this generalization was observed in buffered sea water at a low pH, 7.6. In this case, the O2 uptake of dilute suspensions was greater, per unit number of spermatozoa, than that of dense suspensions. 6. 2,4-dinitrophenol, 6 x 10-5M, stimulated the O2 uptake and depressed the motility of spermatozoa more in dense than in dilute suspensions. Versene, 10-3M, reversed the action of 2,4-dinitrophenol. 7. The results of other workers on adding suspensions of usnic acid to sea-urchin spermatozoa were not confirmed. This substance is more toxic to spermatozoa in dilute than in dense suspensions.