Studies on the mechanism of flagellar motility.

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The movement of eukaryotic cilia and flagella is characterized by rhythmic generation of bending waves. There is ample evidence that mechanical and chemical conditions influence the frequency of the flagellar oscillation, however, no systematic investigation has been made so far on the effect of changing the beat frequency on other parameters of flagellar movement, because no reliable method has been available with which one can either increase or decrease the beat frequency reversibly.Our introduction of imposed head vibration of a sperm (Gibbons et al., 1987) allowed us to manipulate the flagellar beat frequency reversibly. In the present study, the heads of demembranated spermatozoa of the sea urchin Tripneustes gratilla, reactivated at different concentrations of ATP, were held by suction in the tip of a micropipette and vibrated laterally with respect to the head axis. This imposed vibration resulted in a stable rhythmic beating of the reactivated flagella that was synchronized to … More the frequency of the micropipette. The reactivated flagella, which in the absence of imposed vibration had an average beat frequency of 39 Hz at 2 mmol 1^<-1> ATP, showed stable beating synchronized to the pipette vibration over a range of 20-70 Hz. At ATP concentrations of 10-100 mumol 1^<-1>, the range of vibration frequency capable of maintaining stable beating was diminished; increase in the ATP concentration above 2 mmol 1^<-1> had no effect on the range of stable beating. In flagella reactivated at ATP concentrations above 100 mumol 1^<-1>, the apparent time-averaged sliding velocity of axonemal microtubules decreased when the imposed frequency was below the unimposed flagellar beat frequency, but at higher imposed frequencies it remained constant, with the higher frequency being accompanied by a decrease in bend angle. This maximal sliding velocity at 2 mmol1^<-1> ATP was close to the sliding velocity in the distal region of live sperm, possibly indicating that it represents an inherent limit in the velocity of active sliding. The results are consistent with the view that the sliding velocity of axonemal microtubules does not depend solely upon the local concentration of ATP, but is also dependent upon the oscillatory mechanism associated with initiation of new flagellar bends. Less