EFFECT OF BEAT FREQUENCY ON THE VELOCITY OF MICROTUBULE SLIDING IN REACTIVATED SEA-URCHIN SPERM FLAGELLA UNDER IMPOSED HEAD VIBRATION

The heads of demembranated spermatozoa of the sea urchin Tripneustes g ratilla, reactivated at different concentrations of ATP, were held by suction in the tip of a micropipette and vibrated laterally with respe ct to the head axis. This imposed vibration resulted in a stable rhyth mic beating of the reactivated flagella that was synchronized to the f requency of the micropipette, The reactivated flagella, which in the a bsence of imposed vibration had an average beat frequency of 39 Hz at 2 mmoll(-1) ATP, showed stable beating synchronized to the pipette vib ration over a range of 20-70Hz, Vibration frequencies above 70Hz cause d irregular, asymmetrical beating, while those below 20Hz induced inst ability of the beat plane. At ATP concentrations of 10-100 mu moll(-1) , the range of vibration frequency capable of maintaining stable beati ng was diminished; an increase in ATP concentration above 2 mmoll(-1) had no effect on the range of stable beating, In flagella reactivated at ATP concentrations above 100 mu moll(-1), the apparent time-average d sliding velocity of axonemal microtubules decreased when the imposed frequency was below the undriven flagellar beat frequency, but at hig her imposed frequencies it remained constant, with the higher frequenc y being accompanied by a decrease in bend angle, This maximal sliding velocity at 2 mmol l(-1) ATP was close to the sliding velocity in the distal region of live spermatozoa, possibly indicating that it represe nts an inherent limit in the velocity of active sliding, The results a re consistent with the view that the sliding velocity of axonemal micr otubules does not depend solely upon the local concentration of ATP, b ut is also dependent upon the oscillatory mechanism associated with in itiation of new flagellar bends,