Movements of Sodium and Potassium into Epididymal Boar Spermatozoa

The kinetics of sodium and potassium transport through the membrane of epididymal boar spermatozoa was investigated with radioisotopes in vitro. The rate of exchange for both sodium and potassium, expressed as relative specific activity, was much more rapid in undiluted spermatozoa from lower caput epididymis than in undiluted spermatozoa from the cauda. When caput spermatozoa were diluted in plasma from the cauda, the rate of exchange became similar to that of cauda spermatozoa in cauda plasma but the reciprocal treatment produced no change. Likewise, the rate of exchange for potassium was increased in cauda spermatozoa by diluting them with seminal plasma. Dilution of both caput and cauda contents with biological salt solutions similar in composition to respective plasma, decreased the rate of exchange in both cases for both iona. The findings are discussed relative to sperm coating macromolecules.