Calcium-dependent flagellar motility activation in Chlamydomonas reinhardtii in response to mechanical agitation.

Flagellar beating in Chlamydomonas was found to be activated by mechanical stimulation. Immediately after a wild-type cell suspension was vortexed, the average swimming velocity of cells increased from 130 mum/second to 150 mum/second, due to an elevation of flagellar beat frequency from approximately 60 Hz to approximately 70 Hz without detectable change in the flagellar waveforms. This response required outer arm dynein. Treatment with EGTA, Ca(2+)-channel blockers, or mechanosensitive-channel blockers inhibited it. In demembranated and reactivated cell models, a modest increase in Ca(2+) concentration elevated the axonemal beat frequency. These data indicate that the mechanical agitation increases beat frequency because it causes Ca(2+) influx into flagella, which then activates outer arm dynein.