Kinetics of binding of cholecystokinin to pancreatic acini.
In the present study we examined the kinetics of binding of iodinated COOH-terminal octapeptide of cholecystokinin (125I-CCK-8) to its receptors on dispersed acini prepared from guinea pig pancreas. At 37 degrees C, binding of 125I-CCK-8 reached a steady state after 60 min of incubation. Dissociation of bound 125I-CCK-8 was biphasic, indicating that the labeled peptide binds in two distinct states: a rapidly dissociating state and a slowly dissociating state. Binding of 125I-CCK-8 in the rapidly dissociating state was maximal within 3 min of incubation, did not depend on incubation temperature or cellular energy metabolism, could be stripped by 0.5 M potassium thiocyanate, and showed accelerated dissociation with CCK-8 or dibutyrylguanosine 3',5'-cyclic monophosphate (Bt2cGMP). Binding of 125I-CCK-8 in the slowly dissociating state was maximal after 60 min of incubation, was decreased by reducing the incubation temperature or inhibiting cellular energy metabolism, was not stripped by 0.5 M potassium thiocyanate, and did not show accelerated dissociation with CCK-8 or Bt2cGMP. Increasing the concentration of 125I-CCK-8 increased the fraction of radioactivity bound in the rapidly dissociating state. When binding of 125I-CCK-8 reached a steady state, nearly all of the bound radioactivity was in the slowly dissociating state. Computer analysis of the inhibition of 125I-CCK-8 by CCK-8 under experimental conditions where the rapidly dissociating state predominates demonstrated a complete loss of high-affinity binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)
Wank
S A
SA
Digestive Diseases Branch, National Institute of Diabetes, and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Jensen
R T
RT
Gardner
J D
JD
D000818:Animals; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002766:Cholecystokinin / Q000493:pharmacokinetics*; D003485:Cyanates / Q000494:pharmacology; D003995:Dibutyryl Cyclic GMP / Q000494:pharmacology; D004734:Energy Metabolism; D006168:Guinea Pigs; D008297:Male; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D011949:Receptors, Cholecystokinin / Q000378:metabolism; D012016:Reference Values; D012844:Sincalide / Q000493:pharmacokinetics
D003485:Cyanates; D011949:Receptors, Cholecystokinin; D003995:Dibutyryl Cyclic GMP; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D002766:Cholecystokinin; C024835:potassium cyanate; D012844:Sincalide