Effect of zinc ions on structure and distribution of neurotubules (author's transl).

Being interested in factors stabilizing neurotubules (NTs) in situ, we decided to immerse short segments of fresh rat peripheral nerves in buffered solutions containing ZnCl2 in final concentrations up to 10-2 m prior to fixation with buffered osmium or glutaraldehyde, both containing ZnCl2. Zinc treatment resulted in a remarkable structural preservation of NTs after fixation with osmium, though they are not preserved by osmium fixation alone. Cross sections of myelinated nerve fibres show NTs arranged predominantly in compact groups. Within the groups NTs are surrounded or embedded in an electron dense fine granular material. The occurrence of incomplete C-shaped NTs and NT-like densities can be seen. NTs exhibit relatively constant distances and sometimes geometric patterns of arrangement. A lot of intertubule cross bridges and NTs with arms could be observed. In longitudinal section the bridge and arm spacing is seen to be periodic along the tubule axis at about 500 A. Zinc treatment of nerves fixed in glutaraldehyde resulted in the same ultrastructural alterations described above. The resistance of zinc-stabilized NTs to degradation by osmium and the ultrastructural changes induced by zinc are discussed. The results suggest that in the presence of zinc ions osmium-labile NTs are transformed--by disassembly and reassembly--to osmium-stabile microtubules that are not identical with preexisting ones.