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Differential Calcitonin Gene‐Related Peptide (CGRP) and Amylin Binding Sites in Nucleus Accumbens and Lung: Potential Models for Studying CGRP/Amylin Receptor Subtypes
Author(s) -
Aiyar Nambi,
Baker Elayne,
Martin John,
Patel Arunbhai,
Stadel Jeffrey M.,
Willette Robert N.,
Barone Frank C.
Publication year - 1995
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1995.65031131.x
Subject(s) - amylin , calcitonin gene related peptide , nucleus accumbens , calcitonin , calcitonin receptor , endocrinology , medicine , receptor , chemistry , neuropeptide , islet , insulin
Calcitonin gene‐related peptide (CGRP), a 37‐amino‐acid peptide, is a member of a small family of peptides including amylin or islet amyloid polypeptide and salmon calcitonin. These related peptides have been shown to display similar effects on in vitro and in vivo carbohydrate metabolism. The present study was initiated to identify and characterize the binding sites for these peptides in lung and nucleus accumbens membranes prepared from pig and guinea pig. Both tissues in either species displayed high‐affinity (2‐[ 125 I]iodohistidyl 10 )humanCGRPα ([ 125 I]hCGRPα) binding (IC 50 = 0.4–7.7 n M ), which was displaced by hCGRP 8–37 α with equally high affinity (IC 50 = 0.4–7.3 n M ). High‐affinity binding for [ 125 I]Bolton‐Hunter human amylin ([ 125 I]BH‐h‐amylin) was also observed in these tissues (IC 50 = 0.2–6.0 n M ). In membranes from the nucleus accumbens of both species, salmon calcitonin competed for amylin binding sites with high affinity (IC 50 = 0.1 n M ) but was poor in competing for amylin binding in lung membranes. Rat amylin 8–37 competed for [ 125 I]hCGRPα binding with higher affinity (IC 50 = 5.4 n M ) compared with [ 125 I]BH‐h‐amylin binding (IC 50 = 200 n M ) in porcine nucleus accumbens, whereas in guinea pig nucleus accumbens, the IC 50 values for rat amylin 8–37 were 117 and 12 n M against [ 125 I]hCGRPα and [ 125 I]BH‐h‐amylin, respectively. Also, functional studies evaluating the activation of adenylate cyclase and generation of cyclic AMP in response to these agonists indicated that hCGRPα (EC 50 = 0.3 n M ), h‐amylin (EC 50 = 150 n M ), and salmon calcitonin (EC 50 = 1,000 n M ) activated adenylate cyclase, resulting in increased cyclic AMP production in porcine lung membranes that was antagonized by hCGRP 8–37 α. The affinity of hCGRP 8–37 α was similar for all three peptides. The cyclic AMP responses to amylin and salmon calcitonin were significantly ( p < 0.05) lower than that of hCGRPα and not additive, suggesting that they are acting as partial agonists at the same CGRP1‐type receptor in porcine lung membranes. Similar observations were made for guinea pig lung membranes. However, human amylin and salmon calcitonin were weaker than hCGRPα in activating lung adenylate cyclase. None of these peptides activated adenylate cyclase in membranes prepared from the nucleus accumbens of both species. The data from these studies demonstrate both species and tissue differences in the existence of distinct CGRP and amylin binding sites and present a potential opportunity to study further CGRP and amylin receptor subtypes.