The Physiology of Sea-urchin Spermatozoa the Nature and Location of the Endogenous Substrate

Sea-urchin spermatozoa, unlike those of mammals, do not obtain the energy necessary for movement by the enzymatic breakdown of substrates in the external medium. The evidence for this view is twofold: first, these spermatozoa are capable of prolonged activity when suspended in pure sea water; secondly, there is no obvious substrate in the normal external medium, seminal plasma diluted with sea water. Until recently the breakdown of intracellular carbohydrate has been assumed to provide the energy for movement. This assumption is mainly based on measurements of the respiratory quotient by Barron & Goldinger (1941), Hayashi (1946) and Spikes (1948, 1949). These authors do not say in their papers how they measured the respiratory quotient. Dr E. S. G. Barron was kind enough to tell one of us (R.) that he used the direct method; Dr Spikes says in his Ph.D. Thesis (1948) that he also used the direct method. In the absence of further information, Hayashi is assumed to have done the same. Conclusions based on this method, when the medium in which the biological material is suspended is weakly buffered and contains bicarbonate, are of questionable value, as the pH becomes widely different in the two suspensions during measurements. In addition, the possibility that CO2 may influence sea-urchin sperm metabolism must be considered, if only because the respiration of sea-urchin eggs is higher when measured by Warburg's indirect method than when the direct method is used (Laser & Rothschild, 1939). The only other evidence for carbohydrate being the endogenous substrate is Spikes' statement (1949) that glycogen-like material disappears from the spermatozoa of Strongylocentrotus purpuratus and Lytechmus pictus during ageing. At the beginning of the one experiment quoted, the content of glycogen-like material was 29-0 mg./g. dry weight of spermatozoa, while after 12 hr. ageing at 19 C, this had fallen to 8-5 mg./g. dry weight. No figures for oxygen uptake during the ageing period are given, though this can be estimated from information in Spikes' Thesis.