Ca2+ is essential for the motility of plasma membrane-intact, but not of demembranated, hamster spermatozoa.

Extracellular Ca2+ is essential for the flagellar motility of membrane-intact hamster spermatozoa. When suspended in a medium completely free of Ca2+, most spermatozoa quickly lost their motility, and remained motionless until they were transferred back to Ca2+-containing medium. The motility could not be restored after the spermatozoa had been in Ca2+-free medium for more than 2 hr. Unlike membrane-intact spermatozoa, demembranated spermatozoa (spermatozoa without plasma membranes) exhibited active movement in Ca2+-free medium, and their motility was inhibited by Ca2+. In view of these facts, we suggest that the "hyperactivated motility" which membrane-intact spermatozoa display upon capacitation may be due to the activation of a Ca2+-dependent adenylate cyclase (and the resultant increase in intracellular cAMP), rather than being a direct effect of a rise in the intracellular Ca2+ concentration.