Differential effects of guanine nucleotides on [125I]-hCGRP(8-37) binding to porcine lung and human neuroblastoma cell membranes.
Calcitonin gene-related peptide (CGRP) mediates its effects by binding to specific receptors which are positively coupled to adenylyl cyclase. CGRP(8-37), a CGRP fragment devoid of the N-terminal region, was shown to be a competitive CGRP receptor antagonist. Only a limited amount of data exists on the usefulness of this ligand in studying CGRP receptors. In the present study, we used [125I]-hCGRP(8-37) to characterize CGRP receptors in porcine lung and human neuroblastoma cell (SK-N-MC) membranes. [125I]-hCGRP(8-37) displayed specific and high affinity binding in both membrane preparations. Displacement studies using [125I]-hCGRP(8-37) and the agonist CGRP revealed the presence of high and low affinity CGRP binding sites in SK-N-MC cell and porcine lung membranes. Addition of guanylimidodiphosphate [Gpp(NH)p] shifted the competition curve to the right and changed the two affinity states of the receptor to a single affinity in SK-N-MC cell membranes. On the other hand, in porcine lung membranes, the whole competition curve was shifted to the right while maintaining the two affinity states. Thus, our data indicate that the new radioligand [125I]-hCGRP(8-37) is a useful tool for characterizing CGRP receptors and their coupling to guanine nucleotide binding proteins.
Aiyar
N
N
Department of Cardiovascular Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406-0939, USA.
Disa
J
J
Siemens
I R
IR
Nambi
P
P
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism / Q000494:pharmacology*; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006801:Humans; D007457:Iodine Radioisotopes; D008168:Lung / Q000737:chemistry / Q000378:metabolism*; D008916:Miotics / Q000378:metabolism / Q000494:pharmacology*; D009447:Neuroblastoma; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology*; D011869:Radioligand Assay; D018015:Receptors, Calcitonin Gene-Related Peptide / Q000032:analysis / Q000378:metabolism; D013552:Swine; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D006150:Guanine Nucleotides; D007457:Iodine Radioisotopes; D008916:Miotics; D010446:Peptide Fragments; D018015:Receptors, Calcitonin Gene-Related Peptide; C058636:calcitonin gene-related peptide (8-37); D006165:Guanylyl Imidodiphosphate; D019204:GTP-Binding Proteins; D015740:Calcitonin Gene-Related Peptide