title: Characterization of cholecystokinin binding sites in rat cerebral cortex using a 125I-CCK-8 probe resistant to degradation.
abstract: Specific binding sites for cholecystokinin (CCK) have been characterized in a particulate membrane fraction of rat cerebral cortex using a biologically active 125I-labeled derivative of the C-terminal octapeptide of CCK (CCK-8) prepared by reaction with the iodinated form of the imidoester (125IIE), methyl-p-hydroxybenzimidate. The time course of binding to cortical membranes was rapid, temperature dependent, and saturable. Half-maximal binding at 24 degrees C was reached in 30 min and full binding at 120 min. At 37 degrees C there was only a slight increase in 125IIE-CCK-8 bound after 15 min. The addition of a large excess of CCK-8 after 30 min of binding at 24 degrees 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 membranes with increasing concentrations of CCK-8 and other structurally related peptides. CCK-8 displaced 50% of the radioligand at 4 nM, CCK-33 at 10 nM, and gastrin (desulfated CCK-8) at 60 nM. Secretin, a structurally unrelated peptide, was unable to displace the radioligand from cortical membranes at 1.0 microM. Finally, 125IIE-CCK-8 exposed to cortical membranes or to buffers that had previously contained such membranes for 60 min at 24 degrees C bound equally as well to fresh cortical membranes as control radioligand that had not been exposed to the same conditions. Thus the 125I-CCK-8 radioligand used in this study was highly resistant to degradative processes in rat brain tissue.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D002766:Cholecystokinin / Q000378:metabolism*; D006993:Hypnotics and Sedatives / Q000378:metabolism*; D007700:Kinetics; D010446:Peptide Fragments / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011949:Receptors, Cholecystokinin; D012844:Sincalide
chemical_list: D006993:Hypnotics and Sedatives; D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D011949:Receptors, Cholecystokinin; D002766:Cholecystokinin; D012844:Sincalide