VISUALIZATION AND CHARACTERIZATION OF CCK RECEPTORS IN EXOCRINE PANCREAS OF RAT WITH STORAGE PHOSPHOR AUTORADIOGRAPHY

Studies on cholecystokinin (CCK) receptors in rat pancreas are usually performed on homogenates. Using storage phosphor autoradiography, a n ew imaging technique with a high sensitivity and large linear dynamic range, we visualized and characterized CCK receptors in tissue section s of normal rat pancreas. The density of CCK receptors in pancreatic t issue sections from 10 normal rats appeared to be unevenly distributed and variable in serial sections. The binding of labeled CCK-8 was mar kedly inhibited by CCK-8 and CCK-A receptor antagonists, but it was on ly weakly affected by gastrin and CCK-B receptor antagonists. At room temperature the CCK-8 dose-inhibition curve was fitted by a two-site m odel: one with a high-affinity but low-capacity site and another with a low-affinity but high-capacity site. The CCK-8 dose-inhibition curve showed that the inhibition of the variable high-density receptors too k place at a low concentration of CCK-8, while the diffuse low-density receptors were inhibited at the high concentration of 1 mu M CCK-8. B inding of labeled CCK-8 at 37 degrees C was homogeneous with a low aff inity and comprised only 4% of that found at room temperature. In summ ary, an uneven density of CCK receptors in the rat exocrine pancreas w as observed and attributed to the variable expression of high-affinity CCK receptors in pancreatic acini.