Ca2+ and cAMP regulations of microtubule sliding in hyperactivated motility of bull spermatozoa.

To reach and fertilize the egg, mammalian spermatozoa change their flagellar movement in the female reproductive tract, named hyperactivation. The biochemical analyses of the hyperactivated movement using demembranated spermatozoa defined the factors inducing this peculiar movement; namely, large asymmetrical flagellar movement observed in the early stage of the hyperactivation was induced with a high Ca(2+) concentration while large symmetrical flagellar movement in the late stage of the hyperactivation was generated with low Ca(2+) and high cAMP concentrations. Under these conditions, the microtubule sliding of bull sperm flagella was investigated by disintegrating the sperm flagella with MgATP(2-) after extracting their plasma membrane and mitochondria. The large asymmetrical flagellar movement was caused by a long sliding displacement of a fiber of the doublet microtubules. On the other hand, the large symmetrical flagellar movement was generated by a large amount of microtubule sliding by many doublet microtubules.