Cholecystokinin (CCK) assays

Cholecystokinin (CCK) is a peptide that acts as a peripheral hormone and as a central neurotransmitter. To date, two distinct receptors have been identified for CCK using structural and operational criteria; CCK1 and CCK2 (formerly CCKA and CCKB, respectively). In addition, there is the gastrin receptor found in the stomach which has a high structural similarity to the CCK2 receptor, but which displays a different pharmacology. This unit presents two methods for the quantification of selective agonists and antagonists at CCK1 receptors and an assay for CCK2 receptors. In the first tissue, the guinea-pig ileum longitudinal muscle with myenteric plexus, both CCK1 and CCK2 receptors are present in the same preparation. Each receptor is distinguished in this assay using selective agonists and antagonists against the unwanted receptor subtype. The second preparation, the guinea-pig gallbladder, is a classical preparation for studying CCK1 receptor-active compounds in the absence of CCK2 sites.