Identification and Characterization of a Specific Receptor for Cholecystokinin on Isolated Fundic Glands from Guinea Pig Gastric Mucosa Using a Biologically Active125I-CCK-8 Probe

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Abstract
Specific binding sites for cholecystokinin (CCK) have been identified and characterized in fundic glands isolated by collagenase treatment from guinea pig gastric mucosa using a biologically active 125I-labeled derivative of the C-terminal octa-peptide of CCK (125IIE-CCK-8). The time course of binding to these glands was rapid, temperature dependent and saturable. At 24, 30 and 37° C, half-maximal binding was reached at 5 min and full binding at 30 min. The addition of a large excess of CCK-8 after 15 and 30 min of binding at 24° C caused a prompt and rapid decline in radioligand bound showing that the interaction was reversible. There was a progressive decline in the amount of 125IIE-CCK-8 bound to fundic glands with increasing concentrations of CCK-8 and other structurally related peptides. Gastrin II displaced 50% of the radioligand at 1.6nM, CCK-8 at 3.2nM, gastrin I at 16nM, and desulfated-CCK-8 and pentagastrin at 59nM. Secretin did not displace the radioligand from fundic glands at 1.0uM. The binding was also tissue specific as glands isolated from the antral mucosa did not contain specific binding sites for 125IIE-CCK-8. This data provides evidence for specific receptors for CCK on gastric fundic glands that may be involved in the control of acid and pepsinogen secretion.