Changes in guinea pig sperm intracellular sodium and potassium content during capacitation and treatment with monovalent ionophores

Guinea pig spermatozoa were collected from the caudae epididymides in various isotonic solutions and the intracellular sodium and potassium content was determined by atomic absorption spectroscopy. The sperm intracellular Na and K content was found to be influenced by large variations in the extracellular concentrations of these ions. Treatment of spermatozoa suspended in a saline‐based solution with the monovalent ionophores monensin or nigericin caused an approximate 2‐fold increase in the intracellular Na content and a 3–6 fold decrease in the intracellular K content. Incubation of the spermatozoa in a K+‐free minimal culture medium (MCM‐PL) at a pH of 7.6 or 8.3 for 2 hr caused an approximate 2‐fold increase in the sperm intracellular Na content and a 5‐fold decrease in the intracellular K content. The motile spermatozoa incubated for 2 hr at pH 7.6 showed less than 5% acrosome reactions, compared with 30–40% acrosome reactions after incubation at pH 8.3, in response to the addition of 5 mM Ca2+. Changes in the sperm intracellular elemental composition during culture in vitro, which may lead to an acrosome reaction, are discussed.