title: Desensitization of adrenomedullin and calcitonin gene-related peptide receptors in vascular smooth muscle cells--effects of receptor activity-modifying protein.
abstract: Recent researches suggest that adrenomedullin (ADM) and calcitonin gene-related peptide (CGRP) bind to the same calcitonin receptor-like receptors (CRLR), with receptor specificity being determined by a receptor activity-modifying protein (RAMP). Our objective was to explore the significance of CRLR/RAMP hypothesis in cardiovascular tissues through experiments on the phenomenon of desensitization of both ADM and CGRP receptors using cultured rat aortic vascular smooth muscle cells (VSMCs). VSMCs were incubated for 20 min either in serum-free medium (SFM) alone or in the SFM containing vasoactive agonist [10(-8) mol/L ADM, CGRP and proadrenomedullin (PAMP)]. Cells were washed twice and incubated for another 20 min in SFM containing a repetitive agonist ADM or CGRP and 0.5 mmol/L isobutyryl methylxant (an inhibitor of phosphodiesterase). VSMCs were harvested and assayed for cAMP. Exposure of VSMCs to ADM, CGRP, or PAMP alone increased intracellular cAMP generation by 191% (P < 0.01), 385% (P < 0.01) and 67% (P < 0.05), respectively, compared with SFM group. Pre-treatment of VSMCs to ADM or CGRP decreased cAMP generation in response to subsequent stimulation with CGRP by 44% (P < 0.05) and 48% (P < 0.01), respectively. Pre-treatment of VSMCs with 100 nmol/L H-89, a protein kinase A (PKA) inhibitor, abolished the desensitization of CGRP-acting receptor, implying that this desensitization was mediated through PKA. In contrast, there was no attenuation in cAMP response to stimulation with ADM by pre-exposure to ADM or CGRP. Identical results were seen with or without PKA inhibition by H-89. Pre-exposure of VSMCs to PAMP resulted in no change in cAMP generation in response to subsequent stimulation with ADM or CGRP. These results indicate that ADM receptors do not desensitize in VSMCs in contrast to CGRP-receptors, which are desensitized by pre-exposure to ADM or CGRP. These data also suggest that the desensitization phenomenon of ADM is different from that of CGRP.
authors.affiliation: Institute of Cardiovascular Research, First Hospital, Peking University, Beijing 100034.
authors.forename: Y F
authors.initials: YF
authors.lastname: Qi
authors.forename: L
authors.initials: L
authors.lastname: Xue
authors.forename: S B
authors.initials: SB
authors.lastname: Chai
authors.forename: Y R
authors.initials: YR
authors.lastname: Shi
authors.forename: Y Z
authors.initials: YZ
authors.lastname: Pang
authors.forename: C S
authors.initials: CS
authors.lastname: Tang
mesh_terms: D053607:Adrenomedullin; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008565:Membrane Proteins / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D058265:Receptors, Adrenomedullin; D018015:Receptors, Calcitonin Gene-Related Peptide / Q000378:metabolism*; D018000:Receptors, Peptide / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D010455:Peptides; D058265:Receptors, Adrenomedullin; D018015:Receptors, Calcitonin Gene-Related Peptide; D018000:Receptors, Peptide; D053607:Adrenomedullin; D000242:Cyclic AMP; D015740:Calcitonin Gene-Related Peptide