AJP - Gastrointestinal and Liver Physiology, Vol 263, Issue 1 44-G51, Copyright © 1992 by American Physiological Society
ATP induces two cholecystokinin binding affinity states in permeabilized rat pancreatic acini
G. T. Blevins Jr and J. A. Williams
Department of Physiology, University of Michigan, Ann Arbor 48109-0622.
The influence of adenine and guanine nucleotides on cholecystokinin (CCK)
receptor binding was examined in streptolysin O-permeabilized rat
pancreatic acini. Specific binding of tracer to intact acini was 12.1 +/-
0.4% per milligram protein, while permeabilized acini bound 34.6 +/- 2.9%
(n = 7). The increase in binding was also seen when normalized to DNA.
Binding to permeabilized acini was reduced by the presence of 1 mM ATP to
23.0 +/- 1.3%. Analysis of competitive inhibition of tracer binding by
unlabeled CCK-8 was consistent with binding to two affinity states on
intact acini, with the equilibrium dissociation constants for the high
(KdH)- and low (KdL)-affinity states equal to 41 +/- 5 pM and 5.2 +/- 0.4
nM, respectively; permeabilized acini displayed a single binding site with
Kd = 598 +/- 40 pM. In the presence of 1 mM ATP, two states were seen on
permeabilized acini with KdH = 85 +/- 11 pM and KdL = 2.7 +/- 0.6 nM. ATP,
ATP gamma S, GTP, and GTP gamma S all inhibited binding, with half-maximal
inhibition occurring at greater than 1 mM, 21 microM, 5 microM, and 0.4
microM, respectively. GTP gamma S (1 microM) also induced two affinity
states with KdH = 112 +/- 7 pM and KdL = 1.5 +/- 0.2 nM (n = 3). Binding of
CCK to pancreatic membranes was also decreased by ATP, and a similar
regeneration of two binding affinity states was observed. ATP also
decreased binding of [125I-Tyr4]bombesin to permeabilized acini, but in
contrast did not generate two measurable binding affinity states.(ABSTRACT
TRUNCATED AT 250 WORDS)
