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Ca2+ is Essential for the Motility of Plasma Membrane‐Intact, but not of demembranated. Hamster Spermatozoa

Summary: 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.