In situ deflection of tendon cell-cilia in response to tensile loading: an in vitro study

To determine if a correlation exists between tensile loading and the deflection of tendon cell-cilia in situ, rat-tail tendon fascicles were stained for tubulin and mounted in a loading device attached to the stage of a confocal microscope. Individual tendon cells (n = 13) were identified and sequential images taken at 0%, 2%, 4%, 6%, and 8% grip to grip strain. The change in ciliary deflection angle was then measured at each strain level. To determine the ability of cilia to return to their original orientation, additional fascicles were loaded to 6% strain and then unloaded to 0% and tendon cell-ciliary (n = 10) deflection angle measured. There was a weak (r(2) =  0.40) but significant (p < 0.0001) correlation between the change in deflection angle and applied strain. Tensile loading produced a change in deflection angle from 0% to 3% (p =  0.039) and from 3% to 6% (p = 0.001) strain. There was no change (p = 1.000) in deflection angle from 6% to 8% strain. Reducing the strain from 6% to 0% resulted in a change (p =  0.048) in angle towards the pre-load position. However, the angle did not return to the pre-strain position (p = 0.025). These results demonstrate that tensile loading produces in situ deflection of tendon cell-cilia and supports the concept that cilia are involved in the mechanotransduction response of tendon cells.