Tissue stabilizer methods in histochemistry

Quantitative studies in the 1960s established that the tissue disruption and enzyme loss which occurs when unfixed cryostat sections are incubated could be prevented with high concentrations of polyvinyl alcohol without inhibition of enzyme activity. This use of polymeric stabilizers has been largely confined to studies of 'soluble' dehydrogenases in tissue sections. However, optimum conditions for 'soluble' enzymes in cut sections may not be ideal for membrane-bound enzymes or for whole cells, where an over-stabilization of membranes can lead to restricted entry of reagents and thereby low activities. Lower concentrations, or other stabilizers such as Ficoll (a synthetic polysucrose) and collagen polypeptides, have been used in such cases. Suggested criteria for a tissue stabilizer are: (i) The stabilizer should be chemically inert, of defined and constant composition, and generally available; (ii) The tissue must remain structurally intact during the incubation, and the final preparation should look 'clean' and have the proper morphology; (iii) The component being assayed must remain inside the section, and not diffuse into the incubation medium. Ideally, it and any reaction product should remain at their original loci, although it may not always be possible to verify this; (iv) Recorded activities should be comparable to those found in biochemical systems under similar conditions.