Kinky microtubules: bending and breaking induced by fixation in vitro with glutaraldehyde and formaldehyde.

We have employed video-enhanced light microscopy to study alterations of the overall shape of microtubules that are produced by the aldehyde fixation methods commonly employed to study them in vitro. Changes brought about by these methods include deformation and breakage. The severity of the effects depends on the fixative employed and increases with its concentration, and with the time of fixation. The changes are observed under a variety of conditions, such as brief exposure to 3.7% formaldehyde, or somewhat longer exposure to glutaraldehyde at concentrations as low as 0.05%. The observed distortion explains why microtubules usually appear curved or sinuous in electron micrographs while appearing relatively rigid and linear in video-enhanced light microscopy. The observed breakage implies that caution must be used in inferring length distributions from measurements of aldehyde-fixed microtubules.