A new, highly selective CCK-B receptor radioligand ([3H][N-methyl-Nle28,31]CCK26-33): evidence for CCK-B receptor heterogeneity.
[N-methyl-Nle28,31]CCK26-33 (SNF 8702) is a nonsulfated cholecystokinin octapeptide analog that is highly selective for cholecystokinin-B (CCK-B) receptors. Inhibition studies using [125I] Bolton-Hunter-labeled CCK-8 show that SNF 8702 has over 4,000-fold greater affinity for CCK receptors in guinea pig cortex relative to those in guinea pig pancreas. SNF 8702 was tritium-labeled to a specific activity of 23.7 Ci/mmol and its binding properties characterized for guinea pig brain membrane preparations. [3H]SNF 8702 binds to a single site with high affinity (Kd = 0.69-0.90 nM) in guinea pig cortex, cerebellum, hippocampus and pons-medulla. Of these four tissues, the highest receptor density was measured in the cortex (86 fmol/mg of protein) and the lowest in the pons-medulla (22 fmol/mg of protein). In contrast to findings of single-site binding in some brain regions, evidence for CCK-B receptor heterogeneity is observed under other conditions. [3H]SNF 8702 binding to membranes prepared from whole guinea pig brain shows biphasic association kinetics at a concentration of 2.0 nM consistent with the presence of binding site heterogeneity. Binding site heterogeneity is consistently observed for [3H]SNF 8702 binding to guinea pig whole brain membranes in saturation studies where a high-affinity site (Kd = 0.31 nM) is distinguished from a low-affinity site (Kd = 3.3 nM). Binding site heterogeneity is also observed for the midbrain-thalamic region. CCK-B receptor heterogeneity is suggested by the effect of the guanyl nucleotide analogue, guanylyl-imidodiphosphate (Gpp(NH)p), on [3H]SNF 8702 binding to CCK-B receptors in the cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)
Knapp
R J
RJ
Department of Pharmacology, College of Medicine, University of Arizona, Tucson.
Vaughn
L K
LK
Fang
S N
SN
Bogert
C L
CL
Yamamura
M S
MS
Hruby
V J
VJ
Yamamura
H I
HI
D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism*; D051381:Rats; D011949:Receptors, Cholecystokinin / Q000037:antagonists & inhibitors / Q000145:classification / Q000378:metabolism* / Q000502:physiology; D012844:Sincalide / Q000031:analogs & derivatives* / Q000378:metabolism; D013388:Succinimides / Q000378:metabolism; D013552:Swine; D014316:Tritium
C044758:Bolton Hunter-cholecystokinin octapeptide; D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D011949:Receptors, Cholecystokinin; D013388:Succinimides; D014316:Tritium; C066684:SNF 8702; D006165:Guanylyl Imidodiphosphate; D012844:Sincalide