Analysis of Receptor Binding and Quantitative Autoradiography

Abstract

Localizing and quantifying receptors in discrete, small tissue regions requires a method of visualizing these receptors at the light microscopic level combined with a means for measuring receptor number over a wide range. Quantitative autoradiography provides both. This technique requires radioligands with high specific activity that are also very selective for the receptor or receptors in question. A hallmark of such radioligands is a high affinity for the receptor and, usually, a low affinity for other similar receptors. It is also necessary to develop methods to allow selective and measureable labeling of the receptor, similar to any radioligand binding approach. This includes establishing the binding kinetics, both association rate and dissociation rate, under a specific set of conditions and demonstrating the radioligand binds with an appropriate pharmacology. Conditions must also maintain tissue integrity to a sufficient degree to allow identification of particular tissue regions, cellular groupings or nuclei.

It is also possible to demonstrate the functional linkage of receptors to other proteins using the quantitative autoradiographic approach. Receptors linked to G proteins, particularly Gi and/or Go, are especially amenable to this approach. Again, it is necessary to establish optimum conditions for each receptor subtype.

Through the use of these techniques, it is possible to examine receptor localization, density, and functional linkage as well as changes in these parameters during development or due to disease processes or drug treatments. This chapter describes the necessary steps to use these techniques correctly.