Control by the environmental concentration of ions of the potential for motility in Japanese eel spermatozoa

We examined the effects in vitro of the ionic composition of the incubation medium on the acquisition and loss of the potential for motility by the spermatozoa of the Japanese eel (Anguilla japonica). Milt were obtained from 10 males that had been artificially matured by repeated injections of hCG. The percentage of motile spermatozoa in the milt samples varied widely (mean, 53.4 +/- 11.8%; range, 7.4-91.5%) when samples were diluted with a hyperosmotic solution (450 mM NaCl buffered at pH 7.5). The percent motility increased significantly after a 60-min incubation in artificial seminal plasma (ASP), consisted of 149.3 mM NaCl, 15.2 mM KCl, 1.3 mM CaCl2, 1.6 mM MgCl2, and 20 mM NaHCO3, buffered with 20 mM TAPS-NaOH at pH 8.1, or in Ca2+- and Mg2+-free ASP (83.4 +/- 2.5% and 86.1 +/- 2.1%., respectively). A rapid decrease in motility was observed in Kf-free ASP (1.8 +/- 0.7%) and in HCO, free ASP (5.7 +/- 2.2%). The percent motility increased with increasing concentrations and decreased with decreasing concentrations of K+ ions (0-30 mM) and HCO3- ions(0-20 mM) in the ASP. The cycle of acquisition and loss of the potential for motility could be repeated several times by changing the concentrations of K+ or HCO, ions in the ASP. These results strongly suggest that variations in the quality of milt obtained from artificially matured males might be related to the ionic constituents of the seminal plasma. The percent motility of eel spermatozoa could be controlled by adjusting the concentrations of K+ and HCO3- ions in the isotonic incubation medium, irrespective of the initial potential for motility. (C) 2001 Elsevier Science B.V. All rights reserved.