CO_2-inhibition of the amplitude of bending of triton-demembranated sea urchin sperm flagella

Demembranated sea urchin spermatozoa were reactivated in solutions containing KHCO_3 and observed in a covered well slide. Although KHCO_3 itself causes a small inhibition of flagellar beat frequency, the results confirm previous observations of a direct inhibition of flagellar bend angle by CO_2 with no effect of CO_2 on frequency. Observation of the effect of pH on the inhibition of bend angle in solutions containing KHCO_3 indicates that a given concentration of OH^- has a similar effect to the same concentration of HCO^(-)_3, as would be expected if CO_(2-) inhibition results from reaction of CO_2 with protein-NH^(+)_(3) 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.