Immunogold for Protein Location in Chromaffin Cells.

The localization and density of any plasma membrane or intracellular protein in chromaffin cells are prerequisites for those studies designed to elucidate their contribution to cellular function within the adrenal gland and can be achieved only by immunoelectron microscopy. The most popular immunoelectron microscopic techniques involved gold particles conjugated to secondary antibodies, leading to electron-dense markers and the so-called immunogold EM method. Two main immunogold electron microscopic techniques exist: the pre-embedding immunogold, whereby the immunolabeling steps take place before samples are embedded, and the post-embedding immunogold, where the immunolabeling steps take place on embedded and sectioned samples. Pre-embedding immunogold is a very sensitive technique useful for simultaneous observation of labeled tissue at the light and electron microscopic levels. Post-embedding immunogold enables the simultaneous localization of different molecules in the cell using secondary antibodies conjugated with gold particles of different size. In this chapter, we introduce pre-embedding and post-embedding immunogold procedures used for the identification of quantitative changes in a wide range of signaling molecules in different tissues and also discuss the limitations inherent to these approaches.