A novel type of mechanoreception by the flagella of Chlamydomonas

A novel type of mechanosensory mechanism is found in Chlamydomonas reinhardtii. When a cell is captured with a suction pipette and a negative pressure is applied, the cell produces repetitive Ca²⁺ impulses at a frequency of 0.5-1.0 Hz. The impulse frequency increases with the applied pressure. The impulses are produced when the flagella are sucked into the pipette but not when the cell body is sucked in leaving the flagella outside the pipette. Cells with short flagella produce impulses of small amplitude. Thus, the site where the cell senses mechanical stimuli and generates the impulse current must be localized at the flagella. The amplitude, shape and ion selectivity of the pressure-induced impulses are distinct from the all-ornone flagellar current that is evoked by photostimulation. The impulses are possibly produced by a combination of currents passing through mechanosensitive channels and Ca²⁺ channels. This response probably functions to modulate flagellar beating and thereby to regulate the behaviour of the cell.