AJP - Gastrointestinal and Liver Physiology, Vol 255, Issue 1 106-G112, Copyright © 1988 by American Physiological Society
Kinetics of binding of cholecystokinin to pancreatic acini
S. A. Wank, R. T. Jensen and J. D. Gardner
Digestive Diseases Branch, National Institute of Diabetes, and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
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)
