Calcitonin gene-related peptide stimulates adenylate cyclase activity in trout gill cell membranes

CGRP stimulates gill carbonic anhydrase activity in molluscs via a common CT/CGRP receptor

The physiological significance of calcitonin gene-related peptide (CGRP) during biomineralization was investigated by assessing the effect of human CGRP on the carbonic anhydrase activity in gill membranes of the pearl oyster, Pinctada margaritifera. Salmon CT and human CGRP were able to induce a 150% increase of the basal activity. No additive effect was observed suggesting that both activities are mediated by the same receptor. The CGRP-stimulated effect was specific as demonstrated by the inhibition produced by the CGRP antagonist, hCGRP8-37. So, CGRP by its specific action on gill carbonic anhydrase controls the calcification process, an ancient role both in invertebrates and non-mammalian vertebrates.

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

Intermedin, a novel calcitonin family peptide that exists in teleosts as well as in mammals: a comparison with other calcitonin/intermedin family peptides in vertebrates

Endocrine regulation in vertebrates is critical for the adaptation and regulation of homeostasis. The G protein-coupled receptor (GPCR) signaling transduction system represents one of the most ancient forms of cell surface signaling. Recently, comparative sequence analysis has aided in the identification and pairing of a variety of ligand/GPCR signaling systems. Among the ligands of type II GPCRs, the calcitonin family peptides including calcitonin, alpha-calcitonin gene-related peptide (alphaCGRP), betaCGRP, adrenomedullin, and amylin are among the best studied hormones, and the founding member, calcitonin, was originally identified and isolated from teleosts. This unique group of peptides shares a conserved tertiary structure with an N-terminal disulfide-bridged ring. In mammals, these peptides signal through two closely related type II GPCRs and three unique receptor activity-modifying proteins. Recently, based on the analysis of multiple vertebrate genomes, we identified a novel calcitonin/CGRP family peptide named intermedin. Here we show that in humans the five paralogous family genes, calcitonin, CGRP, amylin, adrenomedullin, and intermedin, evolved before the emergence of modern vertebrates, and that teleost genomes carry multiple copies of these co-evolved hormone genes. Sequence comparison showed that each of these genes is highly conserved in different vertebrates and that multiple copies of these peptides in teleosts could be derived from ancient genome duplication and/or lineage-specific intragenic duplications. The present article provides an overview of the calcitonin/intermedin family peptides found in teleost and mammalian genomes, and describes their putative functions. In addition, we demonstrate that one of the intermedin orthologs deduced from the pufferfish (Fugu rubripes) genome shares a conserved signaling activity with mammalian intermedin. The combined results indicate that the physiology associated with each of these family peptides likely evolved during early vertebrate evolution and diverged to serve select physiological functions in different vertebrates.

Characterisation and distribution of calcitonin gene-related peptide in a primitive teleost, the eel, Anguilla anguilla and comparison with calcitonin

Radioimmunoassay (RIA), radioreceptor assay and chromatography were used to study the occurrence of calcitonin gene-related peptide (CGRP) in a primitive teleost, the eel, Anguilla anguilla. Immunologically and biologically active CGRP-like molecules were found in brain, heart, kidney, liver, spleen and ultimobranchial body with the higher concentrations in brain, spleen and heart. Gel exclusion chromatography of heart and spleen extracts followed by SDS-PAGE showed that the eel CGRP-like molecules presented a molecular weight between 3.30 and 3.95 kDa similar to that of human CGRP. The wide distribution of CGRP reflects its multiple role as brain neuromediator and peripheral paracrine effector as described in mammals. In comparison, the distribution of calcitonin (CT) was much more restricted, immunologically and biologically active CT-like molecules being localised in the ultimobranchial bodies (UBB) that is the site of CT synthesis in non-mammalian vertebrates. In plasma, CGRP-like concentrations were 10 to 100 higher than those of CT. These high concentrations in a primitive teleost strengthen the possible endocrine role of CGRP in early vertebrates and emphasise the important role of this hormone in evolution.

Sequencing of a calcitonin receptor-like receptor in salmon Oncorhynchus gorbuscha. Functional studies using the human receptor activity-modifying proteins

The calcitonin gene-related peptide (CGRP) receptor and adrenomedullin (ADM) receptor are generated by the concomitant expression of a calcitonin receptor-like receptor (CL receptor) and a specific receptor activity-modifying protein (RAMP) in mammals. We have identified the sequence encoding the salmon CL receptor (sCL receptor) and studied its function after co-expression with the human RAMPs in Cos-7 cells. The potential open-reading frame encoded a 465-amino-acid protein which is 72% identical to the human CL receptor and 85.8% identical to the flounder CL receptor. Function was assessed by measuring the cyclic adenosine monophosphate (cAMP) produced by Cos-7 cells transiently transfected with recombinant vectors for the sCL receptor and human RAMP. Co-expression of the CL receptor and RAMP1, formed a CGRP receptor, as in mammals. This CGRP receptor responded to selective analogs as a type 1 CGRP receptor. Cells co-expressing the CL receptor and RAMP2 did not produce increased cAMP in response to human ADM. Cells co-expressing the CL receptor and RAMP3, produced such a response, as in mammals, indicating that the human ADM molecule is not the cause of the previous unresponsiveness. We suggest that the human RAMP2 molecule does not interact with the sCL receptor because of major differences in the sequences of the salmon CL receptor and the mammalian CL receptor. The availability of this receptor must allow to further study their structural basis. This identification of a non-mammalian CL receptor, and characterization of its function, give insight in the evolution of the CL receptor molecule.

Effect of calcitonin gene related peptide on the adenylate cyclase activity in abalone gill membranes

The aim of the present study was to investigate and to compare the effect of calciotropic hormones, human calcitonin gene related peptide (CGRP) I and II, salmon calcitonin (CT) and human amylin on the adenylate cyclase activity in abalone gill membranes. In addition to human CGRPI, human CGRPII and salmon CT stimulated the adenylate cyclase activity. No effect was observed with amylin. The higher effect was observed with human CGRPI and II that induced a 160-170% increase of the enzyme activity. Fifty percent of the maximal activity was observed with 3 and 8 nM of CGRP I and II, respectively. Salmon CT induced a lower effect: the maximal activity was obtained with a hormone concentration of 266 nM and represented a 130% stimulation of the basal activity. In the presence of CGRP 8-37, a competitive antagonist of CGRP action, the stimulation observed with CGRPI was abolished and returned to the basal level. This study points out that, in invertebrates, CGRP receptors present in gill membranes are linked to an adenylate cyclase system similar to that described in vertebrates. In addition, these data are in favour of a role for CGRP in branchial function both in non-mammalian vertebrates and invertebrates

Interaction of cysteine proteases with calciotropic hormone receptors

The effect of two cysteine proteases: papain and a cathepsin L-like enzyme purified from the oesophagus of Nephrops norvegicus (NCP) was studied on the specific binding of calcitonin (CT) and calcitonin gene related peptide (CGRP) to rat kidney and liver membranes, respectively. In addition, the response of adenylyl cyclase to increasing concentrations of these two enzymes was investigated. Each protease inhibited the initial CGRP and CT binding to rat liver and kidney membranes, respectively, in a manner not significantly different from that obtained in the presence of the unlabeled standard. The adenylyl cyclase activity in rat liver membranes was increased by the addition of each enzyme. The response was higher with papain that induced a fivefold increase of enzyme activity at a 4-microg/ml enzyme concentration. In rat kidney membranes, the magnitude of the response was identical with both enzymes. In contrast with NCP, papain induced a biphasic response. Leupeptin and E(64), two specific inhibitors of cysteine proteases, reversed the observed effects. Trypsin induced an inhibition of the liver membrane adenylyl cyclase activity and an activation in rat kidney membranes at low protease concentration. Thus, cysteine proteases are able to act, in vitro, at the receptor level in target organs specific for calciotropic hormones.

Calcitonin gene-related peptide (CGRP), but not tachykinins, causes relaxation of small arteries from the rainbow trout gut

Possible vasoactive effects on small diameter arteries from the rainbow trout gut of calcitonin gene-related peptide (CGRP-chicken) and different fish tachykinins; substance P (SP-trout), neurokinin A (NKA-trout), scyliorhinin I and II (SCY I and SCY II-dogfish), were investigated. CGRP relaxed precontracted arteries with a pD2 value of 8.3+/-0.2. Relaxation to CGRP 10(-8) M was reduced by 86.4+/-5.2% by the CGRP-1 receptor antagonist CGRP8-37 (10(-6) M), but unaffected by NG-nitro-L-arginine (10(-4) M), indomethacin (10(-6) M) and by removal of the endothelium, suggesting no involvement of nitric oxide, prostaglandins or endothelium-derived factors. A low number of CGRP immunoreactive fibers were present in the arterial wall. The tachykinins (10(-12)-10(-6) M) occasionally contracted the relaxed vessel. No synergistic action of SP on the CGRP-induced response was found. A dense plexus of tachykinin-containing fibers without coexisting CGRP innervated the arterial wall. Tachykinins or CGRP had no effect on small diameter veins, and no such immunoreactivity was found in these vessels. In conclusion, CGRP- and tachykinin-containing fibers innervate trout gut arteries. CGRP probably is vasodilatory, while the function of the tachykinin fibers is unknown.

Effects of modulatory agents on neurally-mediated responses of trout intestinal smooth musclein vitro

Mediators and mechanisms responsible for the inhibitory modulation of trout intestinal smooth muscle were examined using a series of putative mediators and substances known to modulate neurotransmission in mammalian systems. Frequency response relationships to transmural stimulation and concentration response relationships to 5-hydroxytryptamine, carbachol, and substance P were established on paired segments of rainbow trout intestinein vitro in the presence and absence of putative modulatory agents. Modulation of neurally-mediated contractions of trout intestine was achieved with dibutyryl cyclic AMP and forskolin, agents that increase intracellular levels of cyclic AMP. The effect appears to be at the level of the smooth muscle, since the adenylate cyclase activator, forskolin, inhibited muscarinic and serotoninergic contractions as well as transmurally stimulated contractions. Substance P-induced contractions were unaffected by forskolin. The endogenous agonists/neurotransmitters which would increase cyclic AMP levels in rainbow trout intestinal smooth muscle are as yet unknown. The effects do not appear to be modulated by vasoactive intestinal peptide (VIP), calcitonin, calcitonin gene-related peptide (CGRP), or agents that activate β-adrenoceptors. Prostaglandin E2 (PGE2) and α2-adrenergenic agonists are possible agents which will decrease contractility of the smooth muscle. They were only active in the proximal intestine and on transmurally stimulated contractions. The effects of both PGE2 and α2-agonists appear to be prejunctional, decreasing release of contractile neurotransmitters in the enteric nervous system.

Characterization of binding sites for calcitonin gene-related peptide in the mollusc gill

Target organs for calcitonin gene-related peptide (CGRP) were investigated in Pecten maximus using 125I-labelled human CGRP. CGRP was shown to interact specifically with mantle and gill tissue. Receptor studies using branchial membrane preparations indicated that the binding was time dependent. Scatchard analysis of binding data showed that there was a single class of binding sites. The affinity constant was found to be 0.7.10(8) M-1 and the number of binding sites 2600.10(8)/mg of protein. Salmon CT inhibited the binding of 125I-labelled CGRP to branchial membranes with a lesser efficiency than that of the unlabelled hormone. A 40% inhibition of the 125I-labelled CGRP binding was observed in the presence of 2.6 and 26 nM CGRP and salmon CT, respectively. In addition, 200 nM human CGRP inhibited 25 and 10% of the basal branchial and mantle adenylate cyclase activity, respectively. These data suggest that CGRP participates in the regulation of the branchial function in molluscs probably via a vasoconstrictor role.

Mode of action of calcitonin-gene related peptide in trout gill membranes: evidence for a GTP coupling process

To evaluate the functional relationship between the calcitonin-gene related peptide (CGRP) receptor in trout gills and guanine nucleotide-binding proteins, we investigated the effect of GTP not only on the CGRP stimulated adenylate cyclase activity but also on the human CGRP binding to trout gill membranes. In the presence of 1 microM GTP, the basal and the CGRP stimulated adenylate cyclase activity were increased by 1.8-fold. In addition, GTP decreased the CGRP binding to gill membranes and accelerated the dissociation of bound labeled hormone. Scatchard analysis of the data revealed that the reduction of human CGRP binding by GTP was mainly due to a decrease in the binding affinity with no significant change in the binding capacity. Thus, the binding of CGRP to fish gill membranes activates adenylate cyclase via a guanine nucleotide dependent mechanism, suggesting the involvement of a guanine nucleotide-binding stimulatory protein in the action of CGRP in fishes.

Binding sites of calcitonin gene related peptide (CGRP) to trout tissues

We localized specific binding sites for human calcitonin gene related peptide (hCGRP) in different organs of the trout using labelled human CGRP. Maximal binding was observed in gill and spleen membranes. The binding of 125I-hCGRP was time and temperature dependent. Scatchard analysis of binding data for the spleen and the gills disclosed two binding sites. The constants for the site of high affinity and low capacity (KAM-1 and Bmax (fmol/mg of proteins] were 2.9 x 10(9) for the spleen and 70 and 3.5 x 10(9) for the gill. Salmon calcitonin (sCT) inhibited the binding of 125I-hCGRP to spleen membranes with the same order of potency as hCGRP. In contrast sCT was less effective than hCGRP in suppressing the specific binding of 125I-hCGRP to gill membranes.