Localization of acetylcholinesterase via production of osmiophilic polymers: new benzenediazonium salts with thiolacetate functions

Revisiting staining of biological samples for electron microscopy: perspectives for recent research

This review revisits essential staining protocols for electron microscopy focussing on the visualization of active sites, i.e. enzymes, metabolites or proteins, in cells and tissues, which have been developed 50 to 60 years ago, however, never were established as standard protocols being used in electron microscopy in a routine fashion. These approaches offer numerous possibilities to expand the knowledge of cellular function and specifically address the localization of active compounds of these systems. It is our conviction, that many of these techniques are still useful, in particular when applied in conjunction with correlative light and electron microscopy. Revisiting specialized classical electron microscopy staining protocols for use in correlative microscopy is particularly promising, as some of these protocols were originally developed as staining methods for light microscopy. To account for this history, rather than summarizing the most recent achievements in literature, we instead first provide an overview of techniques that have been used in the past. While some of these techniques have been successfully implemented into modern microscopy techniques during recent years already, more possibilities are yet to be re-discovered and provide exciting new perspectives for their future use.

The cytochemical localization of cholinesterase activity in the developing chick heart

The electronhistochemical localization of the cholinesterases of developing chick heart muscle cells has been studied with the aid of a substrate which incorporates an enzyme-susceptible thiolester group and a diazonium group into the same molecule. The embryonic chick heart exhibits cholinesterase activity from Hamilton-Hambruger stage 3 through to four days post hatching. Although enzyme activity is not demonstrated in every location at all stages studied, it has been observed on the nuclear envelope, golgi complex, rough and smooth endoplasmic reticulum, mitochondria and myofilaments. A change in the type of activity has been demonstrated, acetylcholinesterase is found during the first fourteen days of development but thereafter, non-specific cholinesterase is seen instead. As nerves have not been found in relation to the working myocardium, further support is given to the concept that an acetylcholine-cholinesterase system of myogenic origin is involved in spontaneous contraction. Consideration of the distribution of enzyme within the myocardial cell, raises the possibility that cholinesterase may be concerned in a regulatory mechanism of protein synthesis, a suggestion made previously in connection with liver cells.