Transient flagellar waveforms in reactivated sea urchin sperm.

Flagellar waveforms have been studied during spontaneous stopping and starting transients of sperm of the sea urchin Tripneustes gratilla reactivated at pH 7.7 with 1 mM MgATP2- in the presence of 15 microM free Ca2+. A stopping transient begins abruptly when a reverse bend fails to be initiated at the proper time, and leaves the last-formed principal bend remaining stationary near the flagellar base while the more distal principal and reverse bends all propagate normally to the tip. After a brief quiescent interval lasting 0.5-4 beat periods, the starting transient begins with initiation of a new reverse bend that then propagates nearly normally to the tip. The total duration of stopping and starting transients is about 1.5 beat periods each, much shorter than the duration of the corresponding transients in the flagella of live sperm studied previously. The brief duration of reactivated transients is interpreted to indicate that the response time of the mechanochemical mechanisms regulating the tubule sliding associated with bend propagation is significantly faster than that of the mechanism responsible for Ca2+-induced asymmetry and quiescence.