Abstract
Cell membrane receptors play a central role in controlling cellular
functions, making them the target of drugs for a wide variety of
diseases. This report describes how a recently developed method,
fluorescence intensity distribution analysis (FIDA), can be used
to develop homogeneous, nonradioactive high throughput screening
assays for membrane receptors. With FIDA, free ligand and ligand
accumulated on receptor-bearing membrane vesicles can be distinguished
on the basis of their particle brightness. This allows the concentration
of both bound and free ligand to be determined reliably from a single
measurement, without any separation. We demonstrate that ligand affinity,
receptor expression level, and potency of inhibitors can be determined
using the epidermal growth factor and beta(2)-adrenergic receptors
as model systems. Highly focused confocal optics enable single-molecule
sensitivity, and sample volumes can thus be reduced to 1 microl without
affecting the quality of the fluorescence signal. Our results demonstrate
that FIDA is an ideal method for membrane receptor assays offering
substantial benefits for assay development and high throughput pharmaceutical
screening.
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