Regulation of flagellar bending by cAMP and Ca2+ in hamster sperm

Hamster sperm were immotile in the medium at free Ca2+ concentrations ([Ca2+]) below 1 x 10(-4) M. The flagellum was acutely bent in the opposite direction to the curve of the hook-shaped heads. This phenomenon seemed to be caused by the decrease in the intracellular cAMP concentration, since the cAMP concentration was low at [Ca2+] below 1 x 10(-4) M and increased abruptly at 1 x 10(-3) M, at which sperm were swimming actively. In addition, sperm became motile due to treatment with 8-bromo-cAMP, a membrane permeable analogue of cAMP, in a medium without Ca2+. These results suggested that extracellular Ca2+ is involved in the regulation of flagellar movement via increasing intracellular cAMP concentration. By the treatment with W-13, a calmodulin inhibitor, sperm also became motile, although cAMP concentration remained at a low level. These results suggested that cAMP is not always required for the flagellar movement when the function of calmodulin is depressed.