Calcium-induced asymmetrical beating of Triton-demembranated sea urchin sperm flagella

Asymmetrical bending waves can be obtained by reactivating demembranated sea urchin spermatozoa at high Ca " concentrations. Moving-film flash photography shows that asymmetrical flagellar bending waves are associated with premature termination of the growth of the bends in one direction (the reverse bends) while the bends in the opposite direction (the principal bends) grow for. one full beat cycle, and with unequal rates of growth of principal and reverse bends. The relative proportions of these two components of asymmetry are highly variable. The increased angle in the principal bend is compensated by a decreased angle in the reverse bend, so that there is no change in mean bend angle; the wavelength and beat frequency are also independent of the degree of asymmetry. This new information is still insufficient to identify a particular mechanism for Ca21-induced asymmetry. When a developing bend stops growing before initiation of growth of a new bend in the same direction, a modification of the sliding between tubules in the distal portion of the flagellum is required. This modification can be described as a superposition of synchronous sliding on the metachronous sliding associated with propagating bending waves. Synchronous sliding is particularly evident in highly asymmetrical flagella, but is probably not the cause of asymmetry. The control of metachronous sliding appears to be unaffected by the superposition of synchronous sliding. KEY WORDS calcium " flagella-microtubules- motility " spermatozoa A variety of situations has been found in which the movements of cilia and flagella can be modi-fied, in vitro and presumably in vivo, by free Ca21 ion concentrations in the range of 10 ' to 10-5 M. In the case of sea urchin spermatozoa, reactivated demembranated spermatozoa swim in circular paths of decreasing radius as the Ca21 concentra-tion is increased (12) and the flagellar beat pattern becomes highly asymmetrical. No functional sig-nificance for this behavior is known for sea urchi