Pharmacological characterization of rat amylin receptors: implications for the identification of amylin receptor subtypes.
OBJECTIVE
Amylin (Amy) is an important glucoregulatory peptide and AMY receptors are clinical targets for diabetes and obesity. Human (h) AMY receptor subtypes are complexes of the calcitonin (CT) receptor with receptor activity-modifying proteins (RAMPs); their rodent counterparts have not been characterized. To allow identification of the most clinically relevant receptor subtype, the elucidation of rat (r) AMY receptor pharmacology is necessary.


METHODS
Receptors were transiently transfected into COS-7 cells and cAMP responses measured in response to different agonists, with or without antagonists. Competition binding experiments were performed to determine rAmy affinity.


RESULTS
rCT was the most potent agonist of rCT((a)) receptors, whereas rAmy was most potent at rAMY(1(a)) and rAMY(3(a)) receptors. rAmy bound to these receptors with high affinity. Rat α-calcitonin gene-related peptide (CGRP) was equipotent to rAmy at both AMY receptors. Rat adrenomedullin (AM) and rAM2/intermedin activated all three receptors but were most effective at rAMY(3(a)) . AC187, AC413 and sCT(8-32) were potent antagonists at all three receptors. rαCGRP(8-37) displayed selectivity for rAMY receptors over rCT((a)) receptors. rAMY(8-37) was a weak antagonist but was more effective at rAMY(1(a)) than rAMY(3(a)) .


CONCLUSIONS
AMY receptors were generated by co-expression of rCT((a)) with rRAMP1 or 3, forming rAMY(1(a)) and rAMY(3(a)) receptors, respectively. CGRP was more potent at rAMY than at hAMY receptors. No antagonist tested was able to differentiate the rAMY receptor subtypes. The data emphasize the need for and provide a useful resource for developing new CT or AMY receptor ligands as pharmacological tools or potential clinical candidates.
School of Biological Sciences, University of Auckland, Auckland, New Zealand.
R J
RJ
Bailey
C S
CS
Walker
A H
AH
Ferner
K M
KM
Loomes
G
G
Prijic
A
A
Halim
L
L
Whiting
A R J
AR
Phillips
D L
DL
Hay
D053607:Adrenomedullin / Q000378:metabolism; D065091:Amylin Receptor Agonists; D000818:Animals; D001667:Binding, Competitive; D019556:COS Cells; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D002522:Chlorocebus aethiops; D000242:Cyclic AMP / Q000378:metabolism*; D058228:Islet Amyloid Polypeptide / Q000378:metabolism*; D008297:Male; D051379:Mice; D009479:Neuropeptides / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D058262:Receptor Activity-Modifying Protein 1 / Q000378:metabolism; D058264:Receptor Activity-Modifying Protein 3 / Q000378:metabolism; D018003:Receptors, Calcitonin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism; D058287:Receptors, Islet Amyloid Polypeptide / Q000037:antagonists & inhibitors / Q000378:metabolism*
C499411:Adm2 protein, rat; D065091:Amylin Receptor Agonists; D058228:Islet Amyloid Polypeptide; D009479:Neuropeptides; D058262:Receptor Activity-Modifying Protein 1; D058264:Receptor Activity-Modifying Protein 3; D018003:Receptors, Calcitonin; D058287:Receptors, Islet Amyloid Polypeptide; D053607:Adrenomedullin; D000242:Cyclic AMP; D015740:Calcitonin Gene-Related Peptide