A New, Highly Selective CCK-B Receptor Radioligand ([³H][N-methyl-Nle^28,31]CCK_26-33): Evidence for CCK-B Receptor Heterogeneity

Authors

R. J. Knapp, University of ArizonaFollow
Linda K. Vaughn, Marquette UniversityFollow
S. N. Fang, University of Arizona
C. L. Bogert, University of Arizona
M S. Yamamura, University of Arizona
V J. Hruby, University of ArizonaFollow
H I. Yamamura, University of ArizonaFollow

Document Type

Article

Language

eng

Format of Original

9 p.

Publication Date

12-1990

Publisher

American Society for Pharmacology and Experimental Therapeutics

Source Publication

Journal of Pharmacology and Experimental Therapeutics

Source ISSN

0022-3565

Abstract

[N-methyl-Nle^28,31]CCK_26-33 (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 (K_d = 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 (K_d = 0.31 nM) is distinguished from a low-affinity site (K_d = 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.

Comments

Journal of Pharmacology and Experimental Therapeutics, Vol. 255, No. 3 (December 1990): 1278-1286. Permalink.

Recommended Citation

Knapp, R. J.; Vaughn, Linda K.; Fang, S. N.; Bogert, C. L.; Yamamura, M S.; Hruby, V J.; and Yamamura, H I., "A New, Highly Selective CCK-B Receptor Radioligand ([³H][N-methyl-Nle^28,31]CCK_26-33): Evidence for CCK-B Receptor Heterogeneity" (1990). Biomedical Sciences Faculty Research and Publications. 67.
https://epublications.marquette.edu/biomedsci_fac/67