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Questions And Answer

• Discovery

  CCK is released from I-cells in the small intestine. CCK stimulates gall bladder contraction and pancreatic enzyme secretion. In the central nervous system, CCK is implicated in anxiogenesis, satiety, appetite, nociception, memory, and learning. In 1928, CCK was first described as an inducer of gall bladder contractions derived from the small intestines of dogs and cats. Pig intestine extracts were known to contain a substance called pancreozymin, which stimulated the secretion of pancreatic enzymes. In 1962, a 33-aa peptide isolated from pig intestines was reported to activate both gall bladder contractions (CCK action) and pancreatic enzyme secretion (pancreozymin action). The sequence of porcine CCK/pancreozymin was determined in 1968.;

• Structure

  Human preproCCK consists of 115 aa residues. Bioactive peptides of varying lengths with different N-terminal extensions (CCK-58, CCK-33, CCK-22, CCK-12, CCK-8, and CCK-4) are produced by enzymatic processing. CCK possesses a sulfated tyrosine at the seventh residue from the C-terminus. The C-terminal phenylalanine residue is amidated. In vertebrates, the amino acid sequences of CCKs are highly conserved, particularly in the C-terminal sequence that retains biological activity .;

• Gene, mRNA, and precursor

  The human preproCCK gene, CCK, location 3p22.1, contains five exons. CCK mRNA is 1511 bases in length and encodes a precursor of 115 aa residues. The CCK gene is expressed in the I-cells of the duodenum and small intestine. In rats, Cck is expressed in the brain, heart, lung, kidney, and small intestine.;

• Synthesis and release

  In intestinal I-cells, dietary lipids and proteins are sensed by GPR40 and the calcium-sensing receptor, respectively, resulting in the stimulation of CCK release.;

• Receptors

  The CCK1 receptor (CCK1R) and CCK2 receptor (CCK2R) are GPCRs that have seven transmembrane domains. Human CCK1R consists of 428 aa residues. CCK binds to CCK1R with 500 to 1000 times the affinity and potency of gastrin and nonsulfated CCK. The sulfation of CCK is essential for receptor activation. The dissociation constants (Kd) of CCK-8 and nonsulfated CCK-8 with CCK1R are 1 and 500 nM, respectively.;

• Agonists and Antagonists

  CCK, A-71623, GW-5823. Devazepide, Lintitript, Lorglumide, PD-140548, T-0632.;

• Biological functions

  CCK stimulates contraction of the gall bladder and secretion of pancreatic enzymes via CCK1R. CCK affects the vagal afferent neurons in paracrine and endocrine manners via CCK1R and inhibits gastric emptying and food intake. Insulin secretion is induced by CCK stimulation. In the central nervous system, CCK is implicated in anxiogenesis, satiety, appetite, nociception, memory, and learning.;

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