Role of potassium and pH on the initiation of sperm motility in the European eel.

The role of potassium from the seminal plasma and/or the activation media was examined by selectively removing K from this media, and by testing the use of K channel inhibitors and a K-ionophore. Sperm motility was measured using a CASA system, intracellular K and pH were measured by flow cytometry, and sperm head area was measured by ASMA: Automated Sperm Morphometry Analyses. Sperm motility was notably inhibited by the removal of K from the seminal plasma and by treatment with the K ionophore valinomycin. This therefore indicates that a reduction of K levels in the quiescent stage inhibits further motility. The normal decrease in sperm head area induced by seawater activation was altered by the removal of K from the seminal plasma, and an increase in the pH in the quiescent stage was also induced. Intracellular pH (pH) was quantitatively measured for the first time in European eel spermatozoa, being 7.2 in the quiescent stage and 7.1 post-activation. Intracellular and external pH levels influenced sperm motility both in the quiescent stage and at activation. The alkalinization of the pH (by NHCl) inhibited sperm motility activation, while acidification (by Na-acetate) did not have any effect. Our results indicate that a pH gradient between the sperm cell and the seminal plasma is necessary for sperm motility activation. The presence of the ion K in the seminal plasma (or in the extender medium) is necessary in order to maintain sperm volume, intracellular pH and sperm motility.