Further studies on the ultrastructural localization of a magnesium dependant neutral ATPase in arteries

Summary

A further analysis of the ultrastructural localization of a Mg⁺⁺ dependant neutral ATPase in arteries (thoracic aorta and basilar artery) has been performed in light of recent findings concerning the use of differential fixation and pitfalls in the standard Wachstein-Meisel (W-M) technique. The localization of reaction product was documented following fixation in 5% and 10% formaldehyde and 5% glutaraldehyde, and following incubation in the standard W-M media with ATP, AMP, β-glycerophosphate as substrates. These results were compared to the localization using a modified W-M medium with ATP in which the lead ion concentration was reduced to 1.8 mM. Using the standard W-M procedure, formalin fixation gave a more intense but also a more diffuse (both intra- and extracellular) precipitate of reaction product than glutaraldehyde. The localization to cell structure remained the same in both cases, namely to the outer cell membrane, within its invaginations and in pinocytotic vesicles of both endothelial and smooth muscle cells. Following incubation in a medium with lower lead ion concentration, less extracellular precipitate was found and following glutaraldehyde fixation, very sparse precipitate of reaction product was localized to the cell membrane and its invaginations, often on the cytoplasmic side. The reduction of extracellular precipitate following pre-incubation in 5 mM cystein was believed to be due to inhibition of an unspecific alkaline phosphatase and phosphomonoesterase which had diffused out of the cell following fixation. Cysteine had no effect on the ATPase of the vascular wall. The significance of these results was discussed in light of previous studies on blood vessels and newer insights into this technique.