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more potassium and less sodium than the seminal plasma (Quinn, White & Wirrick, 1965). Similar differences in concentrations of these ions between spermatozoa of marine invertebrates and the sea-water environment have also been reported (Steinbach & Dunham, 1961). Quinn et al. (1965) employed the packed wet cell weight of spermatozoa for calculation of sodium and potassium content of the cells, and on this basis found evidence for active extrusion of sodium and accumulation of potassium by spermatozoa of dog (Quinn & White, 1967), bull and ram (Quinn & White, 1968). Steinbach & Dunham (1961) measured both wet and dry weight of pelleted spermatozoa and thus were able to derive the concentration of alkali cations in the intracellular fluid, assuming the latter to be represented by the difference between wet and dry weight. While this approach has many shortcomings when applied to so unhomogeneous a cell as the mammalian spermatozoon, it does permit estimates of concentration gradients between cell and environment. The present report describes a preliminary investigation of the distribution of sodium and potassium between cell water of bull spermatozoa and an artificial medium in which they were suspended under various metabolic conditions. Fresh samples of bull semen were centrifuged at 1000 g at room temperature for 10 min; the seminal plasma and debris were discarded; and spermatozoa washed twice by repeated centrifugation in an artificial seminal plasma (Na citrate, 38 m-mole; NaCl, 10 m-mole; KC1, 50 m-mole; NaH2P04, 1 m-mole; CaCl2, 6 m-mole; MgCl2, 5 m-mole; fructose, 30 m-mole; pH, 7-2). All subsequent manipulations of the cells employed this medium. For determina¬ tion of extracellular space in pelleted cells, a trace of 14C-labelled sucrose was added to the cell suspension which was then centrifuged at 3000 g for 15 min at room temperature. (The validity of this procedure for the determination of extracellular space was established by repeated washing of the cells with unlabelled medium when the radio-activity of the successive supernatants delivered exponentially, as expected of a single compartment. 14C-labelled inulin and 60Co-EDTA gave the same results). A 5-ml suspension yielded 0-2 g wet pellet in centrifuge tubes fitted with a lower capillary section which

INTRACELLULAR LEVELS OF SODIUM AND POTASSIUM IN BULL SPERMATOZOA IN RELATION TO CELL METABOLISM