Life and Medical Sciences
Cell & Developmental Biology
Wiley InterScience Backfile Collection 1832-2000
Estimates were made of the proportion of freely motile mouse spermatozoa displaying hyperactivated motility by an objective photographic method employing stroboscopic illumination under dark-field conditions and examining displacements of the sperm head and bend angles of the sperm tail. In media known to support in vitro fertilisation hyperactivation gradually appeared reaching about 40% by 6 hr incubation, and it was not promoted by 2 mM caffeine or 0.1 mM Bt2 cAMP or washing the cells free of epididymal fluid. Raising the osmolarity of the medium to 400 mOSM with electrolytes, but not nonelectrolytes, did promote hyperactivation (60% by 2 hr) suggesting that the ionic strength of the medium was important. Hyperactivation in high ionic strength media could be prevented by removing or chelating Ca2+, or replacing Ca2+ with Ba2+ or Mg2+, when nonhyperactivated motility was maintained, but Sr2+, like Ca2+, permitted hyperactivated motility. Hyperactivation in low ionic strength medium could be promoted by the ionophore A23187, suggesting that Ca2+ movement into the cells is important. Of a range of glycolytic substrates tested supporting nonhyperactivated motility in the presence of lactate, only glucose supported hyperactivation. Addition to glucose - or Ca2+ - free, high ionic strength media after 2 hr increased hyperactivation immediately (glucose) or after a lag of 2 hr (Ca2+) suggesting that glucose acts on a Ca2+ - primed system. Removal from high ionic strength medium, chelation of Ca2+ or inhibition of glucose metabolism did not prevent hyperactivation continuing once it had been initiated, indicating different requirements for initiation and maintenance of this form of motility.
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