Demembranated sea urchin spermatozoa were reactivated in solutions containing KHCO3 and observed in a covered well slide. Although KHCO3 itself causes a small inhibition of flagellar beat frequency, the results confirm previous observations of a direct inhibition of flagellar bend angle by CO2 with no effect of CO2 on frequency. Observation of the effect of pH on the inhibition of bend angle in solutions containing KHCO3 indicates that a given concentration of OH- has a similar effect to the same concentration of HCO3-, as would be expected if CO2- inhibition results from reaction of CO2 with protein-NH3+ groups to form carbamates. CO2 may interfere with a control mechanism which selectively suppresses dynein cross-bridge activity in order to generate rhythmic bending. This control mechanism may incorporate a feedback control involving a measure of flagellar amplitude, which fails to operate successfully when the amplitude is reduced below a critical level.

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