Competitive receptor assays applications

Bunce NJ, Hu K, Chittim BG, Tashiro CHM, Yeo BR, Sharratt BJ, Campbell FJ, Potter DW (1995 b), Environ. Sci. Technol. 29 2603-2609.. .Screening assay for dioxin-like compounds based on competitive binding to the marine hepatic Ah receptor. 2. Application to environmental samples"... 

The application of environmentally sensitive chelates have been applied to develop a more straightforward approach to the development of a competitive homogeneous assay. This principle has been applied to some steroid glucuronides (22,23), thyroxine (21) and receptor ligand assays. 

An immediate problem that must be overcome when conducting an RRA is the relatively low density of receptors specific for the ligand vis-a-vis other tissue constituents that are available for nonspecific interactions. Indeed, in many competitive binding assays, the amount of ligand specifically bound when all receptors are occupied (saturated) is on the order of fmoles/mg protein Because m most applications, and particularly for RRAs, non-... 

Antibodies can be used for a variety of applications in the molecular characterization of receptors and receptor-hgand interactions. Antibodies can be used for the detection of receptors in tissue shces. Western blot experiments [48], or ELISAs (enzyme-linked immunosorbent assays) [49]. They can also be used in competition experiments to map the binding epitope of a hgand [50]. Even though the use of antibodies is routine, fhere is no general protocol for fheir generation. 

The best known clinical application of cholinesterase assay concerns the abnormally prolonged effect of the muscle relaxant succinylcholine that is found in a small proportion of patients. This compound, which was introduced into clinical medicine in the early 1950s (B29, B41, T47), owes its relaxant action to competition with acetylcholine for the receptors at the neuromuscular junction both cause depolarization of the muscle fibers, which contract. Acetylcholine is rapidly destroyed by acetylcholinesterase, so that repeated stimuli are applied to the muscle, causing a controlled contraction which persists as long as the nerve is stimulated. When, however, succinylcholine is administered, it is not destroyed by acetylcholinesterase, and its action persists until a large proportion of the dose has been hydrolyzed in the plasma. After initial contraction, the muscle fibers passively elongate to give the relaxation required by the anesthetist. 

A wide variety of commercial LFIA kits for the detection of antibiotic residues is available and the most well-characterised of these are summarized in Table 5.4, including the rapid one-step assay (ROSA) range from Charm Sciences Inc., and the Tetrasensor, Twinsensor, Trisensor, and Sulfasensor from Unisensor SA and the Betastar from Neogen Corporation. Other LFIA assays have been reported in the scientific literature for the detection of antimicrobial residues, including a lateral-flow device for nicarbazin detection in animal feedstuffs. However, at present these are not commercially available. These LFIA tests incorporate either a receptor protein or an antibody as the specific capture molecule and operate in the competitive assay format (most applicable for small-molecule detection). The sample preparation protocols are based on either direct analysis of the liquid sample (e.g., milk) or a simple extraction step for solid or complex matrices using buffer(s) supplied in the test kit. In general, the time required to perform these tests is less than 30 min with only basic laboratory equipment, if any, required. 

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