Effects of divalent and lanthanide ions on motility initiation in rat caudal epididymal spermatozoa.

1 Sperm motility initiation of rat caudal epididymal spermatozoa in vitro has been studied.2 Spermatozoa flushed out from the cauda epididymis with a sodium-free medium exhibited a transient motility which decreased progressively. At 40 min, the forward motility was completely suppressed. However, if they were resuspended in a sodium containing medium their motility was completely restored to normal within 15 min.3 This initiation of sperm motility required the presence of extracellular calcium. Maximal stimulation was obtained at a calcium concentration of 10(-3)M. Above this concentration, further increase in calcium produced a fall in motility and at 10(-2)M, motility initiation was completely suppressed.4 The initiation of sperm motility has been shown to depend closely on sodium. Sperm motility initiation alters in a curvilinear fashion with extracellular sodium concentration showing saturation kinetics. High calcium (above 10(-3)M) was found to depress motility initiation induced by sodium, without affecting the apparent affinity constant for sodium.5 The effect of Ca(2+) on sperm motility initiation could be mimicked by Sr(2+) but not by Mg(2+), La(3+) or Eu(3+).6 In the presence of extracellular calcium (1.27 or 2.54 mM), La(3+) and Eu(3+) exerted a dose-dependent inhibition of sperm motility initiation. The IC(50) values for both ions were about 5 x 10(-5)M.7 The possible mechanism of inhibition by lanthanide ions is discussed.