Regulation of microtubule sliding by a 36-kDa phosphoprotein in hamster sperm flagella

Cyclic AMP has been shown essential for activation of sperm motility. When immotile hamster caudal epididymal spermatozoa were suspended in a Ca2+-def icient solution, they showed a sluggish motility. Spermatozoa were demembra nated and transferred to an ATP-containing reactivation solution. Demembran ated spermatozoa did not exhibit reactivated flagellar movement unless cAMP was added. Conversely, when the immotile epididymal spermatozoa were suspe nded in a Ca2+-containing solution, they were immediately activated to disp lay a vigorous motility; demembranated spermatozoa also exhibited reactivat ed flagellar movement in the reactivation solution without cAMP. Further in vestigation of microtubule sliding properties revealed that the effects of Ca2+ on live spermatozoa were identical with the effects of cAMP on demembr anated spermatozoa both in microtubule sliding velocity and sliding disinte gration pattern. Moreover, a 36-kDa flagellar protein was found to be phosp horylated in a cAMP-dependent manner and coupled to the motility activation . A polyclonal antibody against this protein was developed and showed speci fic immunolocalization and significant inhibitory effects on microtubule sl iding disintegration. These results indicate that extracellular Ca2+ owes i ts effect to triggering intracellular cAMP production, and cAMP-dependent p hosphorylation of a 36-kDa phosphoprotein activates hamster sperm motility through regulation of microtubule sliding properties. Mel. Reprod. Dev. 52: 328-334, 1999. (C) 1999 Wiley-Liss, Inc.