optimal-osmolality of fixative solution
The total or final osmolality of fixative solution mixtures (buffer + fixative + optional additive) has an important effect on tissue morphology and cell organelle distribution.
- Hypertonic solutions cause cell shrinkage (water outflow).
- Isotonic fixatives produce slightly distorted cells and non-optimal fixation, as do hypotonic fixatives.
The best results were obtained with slightly hypertonic solutions (420 to 440 mOsm).
- The effects of the osmotic pressure that the fixation solution develops are even more visible at the ultrastructural level (E.M.) than at the histological level (O.M.) because the semi-permeable phospholipid membranes are easily weakened by solutions that are too hypotonic or hypertonic.
- Normally the osmolarity is chosen according to its osmole value of the internal environment (blood serum for mammals ~320 mOsm, sea water for marine fish ~1000mOsm.).
- By experience, microscopists set their osmolarity a little higher, respectively 390 to 430 mOsm, marine organisms 1100mOsm up to 1350mOsm.
- exemple fixation protocol (Mammifere)
- click images
board of optimal-osmolality fixative solution
