Kinetics of binding of cholecystokinin to pancreatic acini

Am J Physiol. 1988 Jul;255(1 Pt 1):G106-12. doi: 10.1152/ajpgi.1988.255.1.G106.

Abstract

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)

MeSH terms

  • Animals
  • Carbonyl Cyanide m-Chlorophenyl Hydrazone / pharmacology
  • Cholecystokinin / pharmacokinetics*
  • Cyanates / pharmacology
  • Dibutyryl Cyclic GMP / pharmacology
  • Energy Metabolism
  • Guinea Pigs
  • Male
  • Pancreas / cytology
  • Pancreas / metabolism*
  • Receptors, Cholecystokinin / metabolism
  • Reference Values
  • Sincalide / pharmacokinetics

Substances

  • Cyanates
  • Receptors, Cholecystokinin
  • Dibutyryl Cyclic GMP
  • Carbonyl Cyanide m-Chlorophenyl Hydrazone
  • Cholecystokinin
  • potassium cyanate
  • Sincalide