Polarity in spontaneous unwinding after prior rotation of the flagellar beat plane in sea-urchin spermatozoa.

The flagellar beat plane of live and reactivated sea-urchin sperm held by their heads in the tip of a vibrating micropipette will rotate along with the plane of the imposed vibration for up to 10 revolutions in either a clockwise or a counterclockwise direction. Subsequent cessation of the imposed vibration is followed by spontaneous unwinding of the flagellar beat plane. Nearly complete unwinding occurs after prior counterclockwise winding. The unwinding of the beat plane after prior clockwise winding is incomplete, but the number of revolutions that remain unwound affects the response of the flagellar beat plane to a second set of imposed revolutions. The initial angular velocity of spontaneous unwinding is approximately proportional to the number of prior winding cycles, independent of their direction. The maximum initial velocity of unwinding was 27 rad s-1 and 20 rad s-1 for live and reactivated sperm, respectively. These data suggest that the force responsible for unwinding of the beat plane is derived from the elastic distortion of some component in the axonemal structure. The difference in completeness of spontaneous unwinding between the two directions of rotation is consistent with the previously suggested hypothesis that imposed rotation of the beat plane reflects the forced rotation of the central pair within the axoneme.