Molecular characterization of a functional cDNA encoding the rat substance P receptor

Expression and solubilization of a recombinant human neurokinin-1 receptor in insect cells

The human neurokinin-1 receptor has been expressed in insect cells using a recombinant baculovirus. The expression level is about 10 times higher than that obtained in mammalian cells. The recombinant receptor was solubilized with CHAPS, and a PEG precipitation procedure was shown to be effective in regaining high affinity substance P binding. This system should allow large scale purification of the human neurokinin-1 receptor.

Neurotrophic effects of substance P on hippocampal neurons in vitro

The potential neurotrophic effect of substance P-like immunoreactivity present in culture media was assessed in rat embryonic day 18 hippocampal cultures. The neurokinin-1 (substance P) receptor antagonist CP-96345 induced neurotoxicity that was dose dependent and attenuated by addition of substance P or the neurokinin-1 agonist [Sar9,Met(O2)11]-SP. These studies suggest that under some conditions neurokinin-1 receptor stimulation promotes neuronal survival.

Substance P receptor-immunoreactive neurons in the rat neostriatum are segregated into somatostatinergic and cholinergic aspiny neurons

Immunochemical characteristics of neostriatal neurons producing substance P receptor (SPR) were examined in adult rats by double- and triple-immunofluorescence methods. In the neostriatum, SPR immunoreactivity was detected in large and medium-sized aspiny neurons. Virtually all SPR-immunoreactive neurons in the neostriatum contained somatostatin (SS) or choline acetyltransferase (ChAT), but not parvalbumin. All SS- and ChAT-immunoreactive neurons in the neostriatum showed SPR immunoreactivity. The co-existence of SS and ChAT was, however, not found in single neurons expressing SPR immunoreactivity. The present results indicate that neostriatal neurons immunoreactive for SPR are segregated into 2 groups: (1) medium-sized, spiny somatostatinergic, and (2) large, aspiny cholinergic neurons.

Regulation of substance P receptor system in rat striatum by chronic naltrexone treatment

Chronic blockade of opioid receptors by naltrexone increases opioid peptides in the striatum, and up-regulates brain opioid receptors resulting in functional supersensitivity. Striatal SP content was increased 3.5-fold after 8 days of naltrexone treatment relative to control animals. The present study was undertaken to determine whether SP receptors in the striatum and SP receptor-coupled second messenger system are modulated by increased striatal SP content induced by chronic opioid receptor blockade. The binding affinity and capacity of SP receptors, determined using [125I]Bolton-Hunter SP ([125I]BHSP) labeled at Lys3, in striatal synaptosomal membranes were not significantly altered by chronic blockade of opioid receptors. Although the concentrations of [Sar9,Met (O2)11]SP, a NK-1 receptor-specific agonist, and SP(1-7), an aminoterminal major metabolite of SP, required to inhibit half of [125I]BHSP binding (IC50) in striatal synaptosomal membranes were significantly decreased, the IC50s for SP and an NK-2 receptor-specific agonist, [Nle10]NK A (4-10), remained unchanged by chronic naltrexone treatment. The data suggest that naltrexone which has no SP receptor antagonistic action, not only indirectly acts on SP-ergic neurons but also causes a change in the apparent affinity of NK-1 receptor (as reflected by changes in IC50 values) in the striatum. Cellular inositol-1,4,5-trisphosphate [Ins(1,4,5)P3], quantified by a highly sensitive and selective radioreceptor mass assay, was increased in the striatum by 28% relative to control levels. With [3H]Ins(1,4,5)P3 as a ligand, Scatchard analyses of the concentration-dependent saturation curves showed that the density of striatal intracellular Ins(1,4,5)P3 receptors was increased by 53%. The levels of SP and cellular Ins(1,4,5)P3, and the density of Ins(1,4,5)P3 receptors in the cerebellum, used as a positive control, were unchanged by chronic naltrexone treatment. The findings of opiate antagonist-induced increases in SP striatal content and Ins(1,4,5)P3 receptor densities, appear to support the concept of a role of endogenous opioids in the regulation of SP receptor activity. The data also suggest that inter-regulatory mechanisms exist between phospholipase C/phosphoinositide-coupled receptors such as SP receptors, and adenylate cyclase-coupled inhibitory receptors, such as opioid receptors.

Identification of both NK1 and NK2 receptors in guinea-pig airways

1. NK1 and NK2 receptors have been characterized in guinea-pig lung membrane preparations by use of [125I-Tyr8]-substance P and [125I]-neurokinin A binding assays in conjunction with tachykinin-receptor selective agonists ([Sar9Met(O2)11]substance P for NK1 and [beta Ala8]neurokinin A (4-10) for NK2) and antagonists (CP-99,994 for NK1 and SR48968 for NK2). 2. The presence of high affinity, G-protein-coupled NK1 receptors in guinea-pig lung parenchymal membranes has been confirmed. The rank order of affinity for competing tachykinins was as predicted for an NK1 receptor: substance P = [Sar9Met(O2)11]substance P > substance P-methyl ester = physalaemin > neurokinin A = neurokinin B >> [beta Ala8]neurokinin A (4-10). The novel NK1 antagonist CP-99,994 has a Ki of 0.4 nM at this NK1 site. 3. In order to characterize [125I]-neurokinin A binding to guinea-pig lung, the number of [125I]-neurokinin A specific binding sites was increased 3-4 fold by purification of the parenchymal membranes over discontinuous sucrose gradients. The rank order of affinity determined for NK1- and NK2-receptor agonists and antagonists in competition for these sites showed that the majority (80%) of [125I]-neurokinin A specific binding was also to the NK1 receptor. 4. Under conditions where the guinea-pig lung parenchymal NK1 receptor was fully occupied by a saturating concentration of either [Sar9Met(O2)11]substance P (1 microM) or CP-99,994 (2.7 microM), residual [125I]-neurokinin A specific binding was inhibited in a concentration-dependent manner by both [beta Ala8]neurokinin A and SR48968. This result shows that the NK2 receptor is also present in these preparations. 5. Similar studies using guinea-pig tracheal membranes demonstrated that [125I]-neurokinin A specific binding was composed of a NK1-receptor component (60%), inhibited by both [Sar9Met(02)11]substance P and CP-99,994, and a significant NK2-receptor component, inhibited by both [beta Ala 8]neurokinin A andSR48968.6. In summary, these data demonstrate that guinea-pig lung parenchyma and guinea-pig trachea express both NK1 and NK2 receptors.

Aequorin-expressing mammalian cell lines used to report Ca2+ mobilization

Mammalian cells that stably express jellyfish aequorin have been used to report activation of Ca2+ mobilization by cell-surface receptors. Expression of aequorin cDNA (pAEQ) was driven by the cytomegalovirus (CMV) promoter in CHO-K1 and 293 cells. Clonal isolates were obtained which express high levels of apo-aequorin protein, the Ca(2+)-dependent luminescence of which is generated by treatment of living cells with the coelenterate luciferin, coelenterazine. Transient expression of aequorin in COS cells results in even greater abundance of luminescent protein. Aequorin protein is lost from digitonin-permeabilized cells to the same extent and at the same rate as lactate dehydrogenase (LDH), indicating cytosolic location of the indicator. Aequorin expressing cells treated with agonists of endogenous receptors were used in luminescence measurements to demonstrate that the reporter lines offer a highly sensitive and robust means of assaying changes in the concentration of cytosolic Ca2+ ion. Transient co-expression of the substance P receptor in aequorin reporter cells was also performed to demonstrate the feasibility of using this convenient and sensitive assay system for large scale screening of ligands that activate cell surface receptors coupled to increases in intracellular Ca2+.

Two signal transduction mechanisms of substance P-induced depolarization in locus coeruleus neurons

Effects of substance P on cultured neurons of the locus coeruleus of the rat were studied using the whole-cell patch clamp technique. In some cells substance P produced a decrease in a K conductance which showed an inwardly rectifying property. In other cells substance P produced an initial inward current which was accompanied by a conductance increase. The rest of the cells showed responses which were mixtures of the above two responses. The measurement of the reversal potential of the initial inward current after suppressing the voltage-gated Ca and K conductances suggests that it is caused by an increase in a non-selective ionic conductance. In cells loaded with 260 microM GTP gamma S, application of substance P produced an irreversible reduction of the K conductance, while the initial inward current could still be recorded, suggesting that the former is mediated by a G protein, whereas the latter may be activated by a different signal transduction mechanism. The initial inward current was not eliminated by external application of high concentrations of tetrodotoxin, d-tubocurarine or amiloride. Nor was it affected by the intracellular application of cyclic GMP or cyclic AMP.

Substance P and substance P receptor histochemistry in human neurodegenerative diseases

Substance P immunoreactivity is localized in discrete subsets of neurons in the human cerebral cortex and basal ganglia. In the normal human cerebral cortex, a subset of aspiny local circuit neurons in deep cortical layers and the cortical subplate contain preprotachykinin mRNA and substance P immunoreactive. These neurons, which contain NADPH diaphorase (NO synthase) activity, are strikingly depleted in Alzheimer's disease--in contrast to other local circuit neurons--suggesting that they may be an early target of the degenerative process. In the human basal ganglia, substance P immunoreactivity and mRNA are localized in a subset of spiny striatal neurons that project to the internal segment of the globus pallidus. These neurons are enriched in D1 dopamine receptors and dynorphin, and are calbindin and DARP 32 immunoreactive. A separate subset of aspiny striatal local circuit neurons also contain substance P immunoreactivity. Fiber and terminal staining is prominent in the matrix compartment of the ventromedial striatum and persists dorsally as a rim outlining patches that contain lesser amounts of immunoreactivity. Intense fiber and terminal staining is found in the pars reticulata of the substantia nigra. In Huntington's disease, substance P is depleted in the striatum in parallel with the dorsoventral gradient of neuronal loss. Terminal staining is progressively depleted in the pallidum and substantia nigra in tandem with striatal atrophy. Substance P receptor immunoreactivity, defined with two polyclonal antisera raised against synthetic peptides derived from the substance P receptor sequence, intensely labels a subset of large neurons in the nucleus basalis and striatum identical to neurons labeled with choline acetyltransferase and nerve growth factor receptor antibodies (although striatal cholinergic neurons do not contain nerve growth factor receptor immunoreactivity in the human). These cholinergic neurons resist degeneration in Huntington's disease but are sensitive to degeneration in Alzheimer's disease. Less intensely labeled neurons include pyramidal neurons in the hippocampal CA2 field, nonpyramidal neurons in CA1-4, pyramidal and nonpyramidal neurons in deep neocortical layers and in the cortical subplate. Substance P receptor immunoreactivity is not well defined in the human globus pallidus or substantia nigra.

Tachykinin receptors: a radioligand binding perspective

The last decade has witnessed major breakthroughs in the study of tachykinin receptors. The currently described NK-1, NK-2, and NK-3 receptors have been sequenced and cloned from various mammalian sources. A far greater variety of tachykinin analogues are now available for use as selective agonists and antagonists. Importantly, potent nonpeptide antagonists highly selective for the NK-1 and NK-2 receptors have been developed recently. These improved tools for tachykinin receptor characterization have enabled us to describe at least three distinct receptor types. Furthermore, novel antagonists have yielded radioligand binding and functional data strongly favoring the existence of putative subtypes of NK-1 and especially NK-2 receptors. Whether these subtypes are species variants or true within-species subtypes awaits further evidence. As yet undiscovered mammalian tachykinins, or bioactive fragments, may have superior potency at a specific receptor class. The common C terminus of tachykinins permits varying degrees of interaction at essentially all tachykinin receptors. Although the exact physiological significance of this inherent capacity for receptor "cross talk" remains unknown, one implication is for multiple endogenous ligands at a single receptor. For example, NP gamma and NPK appear to be the preferred agonists and binding competitors at some NK-2 receptors, previously thought of as exclusively "NKA-preferring." Current evidence suggests that tachykinin coexistence and expression of multiple receptors may also occur with postulated NK-2 and NK-1 receptor subtypes. Other "tachykinin" receptors may recognize preprotachykinins and the N terminus of SP. In light of these recent developments, the convenient working hypothesis of three endogenous ligands (SP, NKA, and NKB) for three basic receptor types (NK-1, NK-2, and NK-3) may be too simplistic and in need of amendment as future developments occur (Burcher et al., 1991b). In retrospect, the 1980s contributed greatly to our understanding of the structure, function, and regulation of tachykinins and their various receptors. The development of improved, receptor subtype-selective antagonists and radioligands, in addition to recent advances in molecular biological techniques, may lead to a more conclusive pharmacological and biochemical characterization of tachykinin receptors. The 1990s may prove to be the decade of application, where a better understanding of the roles played by endogenous tachykinins (at various receptor subtypes) under pathophysiological conditions will no doubt hasten the realization of clinically useful therapeutic agents.

Functional neurokinin 1 receptors for substance P are expressed by human vascular endothelium

Substance P (SP), a neurotachykinin, is important in a number of inflammatory processes in which the endothelial cell also plays a critical role. SP receptors have previously been identified only on arterial endothelium, and the scant in vitro evidence for direct effects of SP on human endothelium is based on studies using nonarterial cells. To better understand SP's role in inflammation, we sought to identify functional SP receptors on human endothelium in situ and in culture. Autoradiographic ligand binding to human umbilical cord sections demonstrates the presence of SP binding sites with characteristics of the neurokinin 1 (NK-1) receptor (displacement by GTP analogues and the NK-1 specific antagonist CP-96,345) on human umbilical arterial, but not venous, endothelium. In culture, human umbilical venous endothelial cells (HUVECs) and human aortic endothelial cells express low levels of available SP binding sites. However, HUVECs, which are serum starved and refed, undergo a dramatic increase in SP binding. SP binding to starved/refed HUVECs induces a transient increase in intracellular calcium. This calcium flux is dose dependent over appropriate SP concentrations and can be blocked by NK-1 specific antagonists. The proinflammatory effects of SP may be mediated in part through the NK-1 receptor on endothelium.

Amino-aromatic interaction between histidine 197 of the neurokinin-1 receptor and CP 96345

Substance P is a peptide neurotransmitter that binds to the neurokinin-1 receptor and is involved in pain transmission and neurogenic inflammation. Recently, a non-peptide substance P antagonist (CP 96345) has been shown to be effective in animal models of pain and inflammation. An understanding of the molecular interactions responsible for ligand binding will be critical for the development of more specific and selective antagonists for the neurokinin-1 receptor and for the discovery of new antagonists for related G-protein-coupled receptors. Here we report that histidine at position 197 in the fifth transmembrane helix of the human neurokinin-1 receptor binds specifically to CP 96345 but not to peptide agonists. Substitution of His 197 by different amino acids and analysis of structural analogues of antagonists suggest that His 197 is involved in an amino-aromatic interaction with the benzhydryl moiety of CP 96345.

Molecular cloning and characterization of receptors for the mammalian bombesin-like peptides

The bombesin-like peptides comprise a large family of peptides common to both amphibians and mammals that function as growth factors, neurotransmitters, and paracrine hormones. GRP, the mammalian homolog of bombesin and its receptor, as well as NMB, the mammalian homolog of ranatensin, are expressed in human neoplasms and, in particular, in small cell lung carcinomas (SCLC). To better characterize the physiological roles of bombesin-like peptides, our laboratory has cloned the receptors for GRP in murines, rats, and humans. The 3T3 GRP receptor was isolated and characterized using the two-electrode-voltage-clamp analysis and acquorin-emission methods in xenopus oocytes expression system. The rat and human GRP and NMB receptors were cloned by hybridization at low stringency, using the mouse cDNA receptor probe. Sequence analysis of the receptors showed 384 and 390 amino acids for GRP and NMB receptors, respectively. The homology between the two receptors is 60% and between species in the same receptor, 90%. The receptors belong to the 7-membrane spanning domains superfamily. The specific GRP-R antagonist blocked the response to bombesin in oocytes injected with GRP-R, but failed to do so in oocytes injected with NMB-R. The two receptors differ in their distribution of tissue expression. RNA blot and RNase protection analysis showed the same size of mRNA without alteration in the receptors. RT + PCR analysis performed on genomic DNA revealed similarity between normal and cell DNAs, suggesting no major gene deletion or rearrangement. Southern blot analysis indicated the absence of gene amplification. Sequence analysis of the exonic segments of the receptor genes displayed identical amino acids to the respective cDNAs. None of the genes had classic TATAA box. Somatic cell hybrids localized the GRP-R on the X-chromosome and the NMB-R on chromosome 6. The same sequence of normal genes and cDNAs of GRP and NMB receptors, together with the gene characterization, demonstrated that SCLC cell lines do not require a structural change in receptor protein or genomic rearrangement.

Biochemical characterization of two different forms of the substance P receptor in rat submaxillary gland

Studies were designed to examine the basis for the difference in molecular weights of the two proteins detected in membrane preparations of rat submaxillary glands after photolabeling with a radioactive analogue of substance P, 125I-p-benzoyl-L-phenylalanine8-substance P. When the two proteins were separated and individually digested with endoglycosidase F, the relative molecular weight of each protein was reduced by approximately 10,000, indicating that the extent of glycosylation of both proteins is the same. To test whether the difference in their molecular weights can be attributed to a difference in the lengths of the two proteins, photolabeled membranes were treated with carboxypeptidase Y before solubilization to remove from each photolabeled protein the carboxy-terminal portion that extends beyond the membrane. Only one, albeit diffuse, band was now observed that on subsequent deglycosylation with endoglycosidase F was more clearly seen to be a single band, indicating that differing lengths of peptide chains were cleaved from the two proteins. These results permit the interpretation that the difference in the two forms of the substance P receptor present in rat submaxillary glands is due to differences in the length of their carboxy termini.

Tachykinin systems in the spinal cord and basal ganglia: influence of neonatal capsaicin treatment or dopaminergic intervention on levels of peptides, substance P-encoding mRNAs, and substance P receptor mRNA

The aim of the study was to test whether the synthesis of substance P (SP) and that of its receptor (also known as NK1 receptor) are coordinately regulated after chronic pharmacologic intervention in two neural systems, the spinal cord and basal ganglia. In one set of experiments, capsaicin was administered subcutaneously during the early postnatal period (day 3 after birth) to induce degeneration of afferent sensory neurons in the spinal cord. In the other set of experiments, interruption of dopaminergic transmission was achieved by two methods: (a) The neurotoxin 6-hydroxydopamine was used to denervate dopaminergic neurons during the early postnatal period, and (b) haloperidol was used in adult animals to block dopaminergic transmission by receptor blockade. The spinal cord, striatum, or both were used for the quantification of tachykinin [SP and neurokinin A (NKA)] and opioid peptides [[Met5]-enkephalin (ME) and dynorphin A (1-8) (DYN)] by radioimmunoassays. The abundance of total SP-encoding preprotachykinin (PPT) mRNA and SP receptor (SPR) mRNA in spinal cord (C5 to T1 segments), striatum, or microdissected substantia nigra was determined by northern blot or solution hybridization analysis. Amines and their acid metabolites were quantified by HPLC. Capsaicin administration (subcutaneously) during the early postnatal period increased latency in a hot-plate test, decreased SP and NKA levels, increased levels of PPT mRNAs, and did not affect SPR mRNA levels in the spinal cord. Intraspinal SP systems may attempt to compensate for the loss of afferent SP input, whereas spinal cord receptor mRNA levels do not appear to be altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of human T lymphoblast growth by sensory neuropeptides: augmentation of cholecystokinin-induced inhibition of Molt-4 proliferation by somatostatin and vasoactive intestinal peptide in vitro

The effects on proliferation of Molt-4 lymphoblasts of cholecystokinin (CCK-8), somatostatin-14 (SS), vasoactive intestinal peptide (VIP) and substance P (SP) were investigated using different combinations of the peptides, peptide analogs and their antagonists. In vitro proliferation of the cells was measured by a colorimetric assay for cell growth and survival. Results indicate that SP and SP (3-11) stimulated, whereas CCK-8, VIP and SS inhibited, proliferation in a dose-dependent manner (P < 0.05). Unsulfated CCK-8 had no effect on growth of Molt-4 lymphoblasts, and a specific antagonist of CCK, at a concentration 10(-6) M, diminished the inhibitory effect of CCK-8 on Molt lymphoblasts (P < 0.05). This suggests that the inhibitory action of CCK-8 was mediated by peripheral-type CCK receptors. SS and VIP, at equimolar concentrations of 10(-6) M, significantly augmented the CCK-8-induced inhibition of Molt-4 lymphoblast proliferation. However, none of the inhibiting neuropeptides suppressed stimulation of Molt-4 lymphoblast proliferation in response to SP. These data suggest a role of sensory neuropeptides including CCK in modulating human T lymphoblast proliferation during neuroendocrine interactions with the immune system.

Antibodies to the rat substance P receptor: production and characterization

1. A protein A-rat substance P receptor (SPR) fusion protein was genetically engineered and used as an immunogen to raise a polyclonal antiserum to the SPR. The fusion protein was expressed in Escherichia coli driven by the heat-inducible lambda promoter (lambda Pr). 2. The fusion protein was purified using an IgG-Sepharose column, which specifically binds proteins containing the protein A moiety. The IgG fraction obtained after the immunization was cleaved to produce Fab fragments, which were subsequently purified using a fusion protein affinity column. The serum (anti-SPR Fab serum) was analyzed by fluorescence-activated cell sorting (FACS) and immunohistochemistry on both a constitutive cell line for the SPR (AR42J) and a cell line transfected with the SPR (KNRKSPR). 3. Specificity of the antiserum for SPR was confirmed by immunohistochemistry on cells using antiserum that had been preincubated with the protein A fusion protein (blocked). 4. The Ca2+ signal normally observed on stimulation of SPR with SP in AR42J cells and SP binding to KNRKSPR cells was shown to be diminished in the presence of anti-SPR Fab serum. SPR from both cell lines was immunoprecipitated using the anti-SPR Fab serum. The antiserum itself did not induce intracellular Ca2+ mobilization normally observed when cells were incubated with SP. 5. This specific SPR antiserum will be a useful tool to investigate further the mechanisms of SP/SPR interactions.

Distribution of thyrotropin-releasing hormone receptor messenger RNA in the rat brain: an in situ hybridization study

Based on the recent cloning of the mouse thyrotropin-releasing hormone receptor, oligonucleotide probes complementary to the DNA sequence were constructed and used for in situ hybridization studies on the rat brain. Thyrotropin-releasing hormone receptor messenger RNA was found in many areas of the brain, mostly showing high degree of overlap with the distribution thyrotropin-releasing hormone binding sites as previously revealed in autoradiographic studies. Thus, a strong signal was observed in the accessory olfactory bulb, the perirhinal sulcus, the ventral aspects of the hippocampal formation, some amygdaloid nuclei, the diagonal band nucleus, parts of nucleus accumbens, the bed nucleus of the stria terminalis, dorsomedial, lateral and perifornical hypothalamic regions, the septohippocampal nucleus, parts of the vestibular complex, as well as many bulbar motoneurons including the facial, dorsal vagal, ambiguus and hypoglossal nuclei, the superficial layer of the spinal trigeminal nucleus, and motoneurons and dorsal horn neurons in the spinal cord. Cells within one and the same nucleus expressed varying levels of thyrotropin releasing hormone receptor messenger RNA suggesting marked differences in rate of receptor synthesis. Most of these areas receive an input by thyrotropin-releasing hormone-positive nerve endings. Taken together these results suggest that thyrotropin-releasing hormone receptors are mostly localized in the vicinity of the cell bodies which express thyrotropin-releasing hormone receptor messenger RNA and mediate the wide range of actions that have been recorded after administration of exogenous thyrotropin-releasing hormone.

Characterization of NK-1 receptors in guinea pig and rat brain membranes with NK-1 peptides and a non-peptide antagonist

The major finding of the present investigation is the demonstration of different NK-1 receptors in rat and guinea pig brain membranes with CP 96345 (non-peptide NK-1 antagonist) and R-544 (NK-1 peptide antagonist). We used [3H][Sar9,Met(O2)11]SP, the highly selective ligand for NK-1 receptor to compare NK-1 binding sites in rat and guinea pig brain membranes. Scatchard analysis revealed the existence of a single population of [3H][Sar9,Met(O2)11]SP binding sites in both preparations. The affinity and the maximal number of binding sites were found closely similar in rat (Kd 2 nM, Bmax = 37 fmol/mg protein) and guinea pig brain membranes (Kd = 3 nM, Bmax = 25 fmol/mg of protein). The order of potency of neurokinins to inhibit [3H][Sar9,Met(O2)11]SP binding from rat brain (SP > NKA > NKB) was found different of that observed on guinea pig brain (SP > NKB > NKA). Results obtained with [Sar9,Met(O2)11]SP, [beta Ala8]NKA(4-10) and [MePhe7]NKB suggest that selective agonists cannot discriminate between NK-1 receptors of different species. Using the non-peptide antagonist CP 96345 and the tripeptide R-544, we found that these two NK-1 antagonists discriminate between rat and guinea pig [3H][Sar9,Met(O2)11]SP binding sites.

The NK1 receptor is involved in the neurokinin-induced shape change of rabbit platelets

Substance P and selective neurokinin receptor agonists have been tested for their ability to induce shape change in rabbit platelets. Substance P and the NK1 receptor agonist Ac [Arg6,Sar9,Met(O2)11]-substance P (6-11) induced shape change (EC50 = 3 and 6 nM, respectively), whereas the selective NK2 agonist [Nle10]-Neurokinin A (4-10) and the selective NK3 agonist [MePhe7]-Neurokinin B did not show any effect. Moreover, the specific NK1 receptor antagonist CP-96,345 selectively and dose-dependently counteracted the effect of substance P or of the NK1 receptor agonist (IC50 = 2 and 0.8 nM, respectively), whereas the selective NK2 receptor antagonist, SR 48968, had no effect. Unlike for serotonin or low doses of ADP, epinephrine did not allow substance P or the NK1 receptor agonist to become a proaggregating substance. These data therefore show that the NK1 receptor is solely involved in the neurokinin-induced shape change of rabbit platelets.

The relationship of calbindin-containing neurons with substance P, Leu-enkephalin and cholecystokinin fibres: an immunohistochemical study in the rat thalamus

In the rat thalamus, immunoreactivity for the calcium binding protein calbindin (Cb) is mostly confined to neuronal cell bodies, sometimes revealing proximal dendrites, of the midline, intralaminar and posterior regions. Substance P (SP)-, cholecystokinin (CCK)- and Leu-enkephalin (L-ENK)-immunoreactive (ir) elements in the thalamus are fibre-like structures, intermingled with punctate elements probably representing axonal arborizations and their synaptic boutons. These peptidergic fibres are unevenly distributed in several thalamic domains, including the areas that contain Cb-ir neurons. The relationship between Cb-ir cell bodies and these three different peptidergic systems of thalamic innervation was studied with immunohistochemistry. Single-labelling experiments on adjacent sections and double immunostaining on the same section were performed. A considerable overlap between Cb-ir perikarya and SP-ir fibres was found in most thalamic nuclei. In particular, in the intralaminar nuclei and posterior complex, SP-ir punctate elements were frequently observed in close proximity to Cb-ir cell bodies and dendrites. On the other hand, no consistent topographical correspondence between Cb-ir perikarya and CCK- or L-ENK-ir fibres was evident. Altogether, the present data suggest a selective anatomical and, possibly, functional relationship between SP and Cb in at least a subpopulation of rat thalamic neurons.

Effects on the isolated human bronchus of SR 48968, a potent and selective nonpeptide antagonist of the neurokinin A (NK2) receptors

Tachykinins produce concentration-dependent contraction of the human isolated bronchus by stimulation of receptors that belong to the NK2 type. The aim of this study was to investigate the inhibitory effects of a new, potent, and selective nonpeptide antagonist of the neurokinin A (NKA) (NK2) receptors, SR 48968 [(S)-N-methyl-N-[4-acetylamino-4-phenylpiperidino-2-(3,4-dichlorophenyl) butyl]benzamide] on human isolated airways. Our experiments were performed on human isolated bronchi obtained from patients with lung cancer. Phosphoramidon, 10(-5) M, was added to the bath to inhibit neurokinin metabolism. SR 48968 induced a parallel shift to the right of the concentration-response (C/R) curves to [Nle10]-NKA(4-10), a specific NK2 receptor agonist. The antagonism was of the competitive type, with a pA2 of 9.40 +/- 0.19 (slope = 0.95 +/- 0.08, n = 13). The (R)-enantiomer of SR 48968 was 100-fold less potent and a noncompetitive antagonist (slope = 0.56 +/- 0.11, n = 8); pA2 and slope of the racemate were 8.86 +/- 0.21 and 1.09 +/- 0.21 (n = 7), respectively. Under similar conditions, racemic CP-96,345, a nonpeptide NK1 antagonist, did not modify the C/R curves to [Nle10]-NKA(4-10) until 10(-7) M. SR 48968 did not modify C/R curves to acetylcholine, histamine, KCI, or PGF2 alpha on the human isolated bronchus. Finally, SR 48968 shifted to the right C/R curves to substance P on isolated human bronchi, whereas racemic CP-96,345 was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Site-directed mutagenesis of the human dopamine D2 receptor

Based on amino acid sequence and computer modeling, two conflicting three-dimensional models of the dopamine D2 receptor have been proposed. One model (Dahl et al., 1991, Proc. Natl. Acad. Sci. USA 88, 8111) suggests that dopamine interacts with aspartate 80 of transmembrane (TM) 2 and asparagine 390 of TM6 with the transmembranes arranged in a clockwise manner, while a second model (Hibert et al., 1991, Mol. Pharmacol. 40, 8) suggests that dopamine interacts with aspartate 114 of TM3 and the serines of TM5 (194 and 197) with the transmembranes arranged in a counterclockwise manner when viewed from the extracellular space. The present study tests the latter model by selectively mutating aspartate 114 and serines 194 and 197 of the human dopamine D2 receptor by site-directed mutagenesis. In addition, two methionines (116 and 117) were mutated to evaluate whether residues near aspartate (114) of the dopamine D2 receptor are critical in differentiating dopamine receptor agonists from adrenoceptor agonists. Removal of the negative charge with the mutation of aspartate (114) to either asparagine or glycine led to a total loss of both agonist and antagonist binding. Individual or dual methionine mutations in positions 116 and 117, to make the dopamine D2 binding pocket more closely resemble the beta 2-adrenoceptor, did not result in a change in selectivity toward noradrenergic agonists or antagonists. The serine mutations revealed interesting differences between the dopamine D2 receptor and the adrenoceptors. In particular, serine 197 appeared more important than serine 194 for agonist binding. In addition, the binding of one agonist (N-0437) was unaffected by individual serine mutations, while the binding of some antagonists, such as raclopride and spiperone, was significantly altered. These findings are discussed in relation to ligand structure and their interactions with the putative binding pocket.

Contrasting effect of substance P on renal function and dopamine excretion in hydropaenic and volume expanded dogs

1. Substance P (SP) and dopaminergic nerves have been described in the kidney. In the brain, SP increases dopamine production. In the kidney, SP increases sodium excretion. 2. Intrarenal dopamine acts as an endogenous natriuretic hormone. It is possible that dopamine could mediate the natriuretic effect of SP. 3. We therefore studied the effect of the intrarenal arterial infusion of SP (0.1, 1.0, 10 ng kg body wt-1 min-1) on mean arterial pressure (MAP), renal blood flow (RBF), glomerular filtration rate (GFR), urine flow rate (V), absolute (UNaV) and fractional (FENa) sodium excretion as well as dopamine and noradrenaline excretion in dogs. Since dopamine is not natriuretic in hydropaenic states, studies were performed during hydropaenic and saline loaded states. 4. During hydropaenia, SP increased RBF, GFR, and V in a dose-related fashion but did not alter UNaV or FENa. Urinary noradrenaline was not affected but urinary dopamine decreased with increasing doses of SP. MAP was not affected. 5. During saline loading, SP increased RBF, GFR, V, UNaV, and FENa in a dose-related fashion. Both urinary noradrenaline and urinary dopamine increased. The fractional excretion of sodium correlated with dopamine but not noradrenaline excretion. MAP was not affected. 6. The renal haemodynamic and functional effects of SP may be mediated by SP-associated increases in urinary dopamine.

The structure of neuropeptide receptors

Recently, the primary structures of 17 different receptors for neuropeptides and small peptide hormones have been elucidated by molecular cloning. All but one belong to the superfamily of G-protein coupled receptors which share a topography consisting of seven transmembrane domains. Comparison of primary structures shows that two classes of peptide receptors exist. One referred to as the 'neurokinin-type receptors', possesses many of the typical, conserved amino acid sequence motifs of the aminergic transmitter receptors (e.g. beta-adrenoceptor). The other, referred to the 'secretin-type receptors', displays unrelated and distinctly different sequence motifs which are conserved between the three presently known members of this class. These are the secretin, calcitonin and parathyroid hormone/parathyroid hormone-like polypeptide receptors. One may speculate that many other peptides with a core of biological activity in the N-terminal or middle region may have receptors of the secretin-type.

Modulatory role of glutathione on mu-opioid, substance P/neurokinin-1, and kainic acid receptor binding sites

Reduced glutathione (L-gamma-glutamyl-L-cysteinylglycine; GSH) is an endogenous tripeptide involved in the formation and maintenance of protein thiol groups as well as in various detoxification reactions. Because multiple receptor types contain thiol groups or disulfide bridges, effects of GSH treatments on mu-opioid, neurokinin-1/substance P, and kainic acid receptor binding sites were investigated and compared with those produced by dithiothreitol (DTT), a potent synthetic reducing agent. GSH inhibited binding more potently than did DTT at all three receptor types in porcine striatal membrane homogenates as well as in CHAPS-solubilized preparations of the mu and neurokinin-1 sites. GSH-induced inhibitory effects were associated with decreases in maximal binding capacity (Bmax) without significant alteration in apparent affinity (KD). Cysteine, the functional moiety of GSH, mimicked GSH effects albeit with lower potencies, whereas oxidized glutathione had no effects at similar concentrations. In CHAPS-solubilized preparations, the combination of low concentrations of GSH and guanylylimidodiphosphate markedly decreased the Bmax values of the binding of [3H][D-Ala2,Gly-ol5]enkephalin and [3H]substance P. This GSH-mediated mechanism may be important to prevent cell overstimulation by accelerating receptor uncoupling, desensitization, and/or internalization. This is in keeping with purported roles of GSH related to the maintenance of cellular integrity.

Ligand binding kinetics of substance P and neurokinin A receptors stably expressed in Chinese hamster ovary cells and evidence for differential stimulation of inositol 1,4,5-trisphosphate and cyclic AMP second messenger responses

Stably transfected Chinese hamster ovary cells expressing either the substance P receptor or neurokinin A receptor were constructed, isolated, and characterized. Equilibrium ligand binding studies performed on whole cells demonstrated that cell lines expressing either of these receptors contained a single class of high-affinity binding sites with an apparent KD of 0.16 nM for the substance P receptor and an apparent KD of 2.1 nM for the neurokinin A receptor. The higher affinity of substance P for its receptor was accounted for by both a greater association rate constant and a lesser dissociation rate constant. The time course and extent of ligand-stimulated inositol 1,4,5-trisphosphate mass increases in both cell lines were similar and displayed rapid and transient kinetics. Ligand-stimulated cyclic AMP accumulation was also apparent in the cell lines, although the time course and magnitude of the responses were substantially different, with the neurokinin A receptor mediating a greater and more prolonged response. These studies establish the presence of functional substance P receptors and neurokinin A receptors in the stably transfected cell lines and provide evidence for agonist-dependent differential stimulation of second messenger responses.

Tachykinin-stimulated inositol phospholipid hydrolysis and taurine release from human astrocytoma cells

The activation of NK1 receptors on U373 MG human astrocytoma cells by substance P (SP) and related tachykinins was accompanied by an increase in taurine release and an accumulation of inositol phosphates. Both of these effects could be inhibited by spantide, a SP receptor antagonist. The relative potency of tachykinins in stimulating 3H-inositol phosphate accumulation correlated very well with their effects in stimulating the release of [3H]-taurine and inhibition 125I-Bolton-Hunter reagent-conjugated SP binding. The effect on [3H]taurine release was mimicked by a protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA). The inactive phorbol ester analogue 4-alpha-phorbol 12,13-didecanoate, however, was without effect. Both SP- and PMA-induced releases of [3H]-taurine were markedly inhibited by staurosporine, a potent PKC inhibitor. Pretreatment of U373 MG cells with 10 microM PMA for 19 h to down-regulate PKC activity also markedly inhibited both SP- and PMA-induced releases of [3H]-taurine. Treatment of cells with 100 nM SP induced a time-dependent translocation of PKC from the cytosolic fraction to the membrane fraction. These findings are consistent with the hypothesis that an activation of NK1 receptors on U373 MG cells results in the release of inositol phosphates and activation of PKC, which in turn may regulate the release of taurine.

The mas proto-oncogene is developmentally regulated in the rat central nervous system

The mas proto-oncogene encodes a protein with a predicted structure similar to members of the family of seven transmembrane domain spanning receptors. These receptors are thought to transduce extracellular signals to G-proteins. Angiotensin II and III have been reported to be the functional ligands for the mas oncogene-encoded receptor (Jackson et al., 1988). We show here using in situ hybridization histochemistry and RNase protection assays that mas mRNA is expressed in a subpopulation of neurons in both the adult and developing rat CNS. In the adult CNS, mas mRNA is most abundant in hippocampal pyramidal neurons and dentate granule cells; mas transcripts are also present at low levels in the cortex and thalamus. mas is first expressed in the developing rat CNS at postnatal day 1 (P1). Even at this early stage in CNS development the pattern of mas expression is similar to that seen in the adult. Although at P1 most neurons of the dentate gyrus are not yet generated and cells of the hippocampal CA fields are undergoing migration and synaptogenesis (Bayer 1980; Altman and Bayer, 1990a, 1990b, 1990c), mas is specifically expressed in these cell populations. This extremely restricted pattern of expression suggests that mas may function in determining the morphology and connections of specific cell types in the hippocampus. This function may in part be carried out by the ability of mas to link external cues to intracellular processes.

Fast and slow depolarizations produced by substance P and other tachykinins in sympathetic neurons of rat prevertebral ganglia

Using intracellular recording, we examined the effects of three mammalian tachykinins, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), on sympathetic neurons of isolated rat coeliac-superior mesenteric ganglia (C-SMG). The 3 tachykinins elicited two distinct depolarizing responses in ganglion cells: fast depolarization with time-to-peak of 1-2 sec and duration of 5-10 sec, and slow depolarization with time-to-peak of about 20 sec and duration of 120-140 sec. Both fast and slow responses persisted in a solution containing low Ca2+ and high Mg2+ or tetrodotoxin, which indicates that the tachykinins directly act on ganglion cells to produce fast and slow depolarizations. The two types of tachykinin-induced responses exhibited clearly distinguishable properties. The membrane conductance was increased during the fast response, but not significantly changed, slightly decreased or sometimes increased during the slow response. Within certain range of membrane potential, the amplitude of fast response increased upon membrane hyperpolarization and decreased upon depolarization of ganglion cells. In contrast, the amplitude of slow response associated with membrane conductance decrease was increased with membrane depolarization and decreased with hyperpolarization. The fast response was markedly suppressed in a Na(+)-deficient solution, a solution containing nominally zero Ca2+ (plus 0.1 mM EGTA in some cases), and in a solution containing Cd2+ or Mn2+, whereas the slow response was not affected in these solutions and was augmented in some cells in K(+)-free solution. Thus it seems that the increase in Ca(2+)-dependent cationic conductance underlies the fast response and that the slow response is produced at least in part by suppression of certain K+ channels. The fast response progressively decreased in amplitude upon repeated application of the peptides with short intervals, whereas the slow response was rather augmented by repeated application. Lowering the temperature markedly depressed the slow response, while the fast response remained almost unaffected. It is therefore likely that the fast and slow depolarizations are mediated by two different subtypes of tachykinin receptors or a single class of receptors linked with two different intracellular mechanisms. Measurement of tachykinins in several sympathetic ganglia by combined use of HPLC and radioimmunoassay revealed that the highest amount of SP occurs in the C-SMG where the content of SP (136.0 pmol/g protein) was higher than those of NKA (44.3) and NKB (18.7). SP thus appears to function as a major tachykinin in rat C-SMG.

Structure, functions, and mechanisms of substance P receptor action

Substance P is a member of a family of structurally related peptides, called tachykinins, that are involved in the regulation of many biologic processes. Diversity in the generation of multiple tachykinin peptides arises due to multiple genes encoding these peptides as well as by mechanisms of alternative RNA processing and differential posttranslational processing. The multiple peptides are neurotransmitters and/or neuromodulator substances, and they bring about their actions mainly by activating three primary types of receptors, NK-1, NK-2, and NK-3. The pharmacology and tissue locations of these receptor sites are discussed, as is their involvement in certain biologic responses. These three receptor sites have been molecularly characterized by cDNA cloning and functional expression, and all are members of the superfamily of receptors coupled to G-regulatory proteins. Second messenger systems established to be activated by tachykinin receptor stimulation include the hydrolysis of inositol containing phospholipids by a phospholipase C mechanism. The role of substance P in neurogenic inflammation and plasma extravasation is briefly discussed. The generation of new research tools recently in the tachykinin field should allow for a detailed examination of the mechanisms of peptide action, including a focus on receptor structure-function relations and regulation of receptor sensitivity.

A combined evaluation of biochemical and morphological changes during human neuroblastoma cell differentiation

1. The effects of retinoic acid, gamma-interferon, cytosine arabinoside, nerve growth factor, tumor necrosis factor, and 12-O-tetradecanoylphorbol 13-acetate on the human neuroblastoma cell line, LAN-5, were studied. Intracellular levels of acetylcholinesterase, neuron-specific enolase, catecholamines and related neurotransmitters, vasointestinal peptide, and substance P were evaluated after induction. 2. Cell morphology was strongly affected by retinoic acid, gamma-interferon, cytosine arabinoside, and 12-O-tetradecanoylphorbol 13-acetate. The main effects of retinoic acid and gamma-interferon were the loosening of cell clusters and the extension of long neurites; cytosine arabinoside induced cell body swelling and marked neuritogenesis. Following 12-O-tetradecanoylphorbol 13-acetate treatment, the cells became small, round, and neuritic. Conversely, modifications induced by nerve growth factor and tumor necrosis factor were mild. Cell proliferation rate was reduced by retinoic acid, gamma-interferon, cytosine arabinoside, and 12-O-tetradecanoylphorbol 13-acetate, while nerve growth factor and tumor necrosis factor were devoid of effects. 3. Acetylcholinesterase activity was significantly stimulated by retinoic acid and by gamma-interferon. Neuron-specific enolase activity was unaffected by all treatments except 12-O-tetradecanoylphorbol 13-acetate, which enhanced it by 1.6-fold. 4. The cellular catecholamine and related metabolite content was lowered by retinoic acid and gamma-interferon, while cytosine arabinoside and, even more, 12-O-tetradecanoylphorbol 13-acetate showed a stimulatory activity on their intracellular accumulation. 5. Finally, the cell-associated vasointestinal peptide level was strikingly increased by gamma-interferon and, to a lesser extent, by retinoic acid, cytosine arabinoside, and 12-O-tetradecanoylphorbol 13-acetate. 6. It is concluded that the most relevant biochemical changes associated with LAN-5 cells differentiation involve the repertoire of neurotransmitters and neuropeptides. These events vary in quality and in quantity, likely due to the pattern complexity of gene expression triggered by each inducer in determining the diversity of neuronal phenotypes.

Neurokinin A (NK2) receptor revisited with SR 48968, a potent non-peptide antagonist

SR 48968, a new non-peptide antagonist of NK2 receptors, has been tested in a variety of isolated smooth muscle preparations from rats, guinea pigs, rabbits, hamsters and men, in order to assess its selectivity for NK2 receptors as well as its competitivity and specificity. The compound has been found to be inactive as a stimulant or relaxant in all preparations but to exert a potent, competitive antagonism, particularly in tissues obtained from rabbits (pA2 9.8-10.3), guinea pigs (10.5), rats (9.4-9.6), men (9.36-9.6) and hamsters (7.45-8.6). SR 48968 is therefore more active on the NK2A than on the NK2B receptor subtype and the human receptor is close to the NK2A subtype. SR 48968 exerts an antagonism of the competitive type and is therefore suitable for receptor classification despite its slow reversibility in vitro. The sensitivity of NK2A receptors to SR 48968 is at least 1000 times higher than those of NK1 and NK3 receptors. The compound does not affect the effects of bradykinin, angiotensin or bombesin. Because of its activity in human tissues, its potency and long duration of action, SR 48968 is a new promising pharmacologic and possibly therapeutic agent.

Molecular cloning of substance P receptor cDNA from guinea-pig uterus

A cDNA encoding guinea-pig uterine substance P (SP) receptor has been isolated using the homology screening approach. Northern blot analysis reveals that the corresponding mRNA, of approx. 4.8 kb, is expressed in all tissues tested, but predominantly in the uteri of non-pregnant animals; during pregnancy its expression is reduced. The guinea-pig SP receptor was expressed in COS-7 cells and demonstrated relative ligand affinity in the order: SP much greater than neurokinin A greater than neurokinin B.

Development of substance P receptors on rat motoneurons in vitro

Experiments were performed to examine the influence of interneuronal interactions on the expression of neurotransmitter receptors by developing mammalian CNS neurons. Receptors for the neuropeptide, substance P (SP), were assayed on embryonic rat motoneurons and other spinal cord neurons developing in vitro by the binding of 125I-SP to live neurons. Scatchard analysis showed the presence of high-affinity binding sites, and binding competition assays using SP, neurokinin A, or neurokinin B indicated that the high-affinity 125I-SP binding sites on these neurons were type NK1 tachykinin receptors, or SP receptors (SPRs). Neurons in the spinal cords of rats at Embryonic Day 14 displayed no SPRs. Cell-surface SPRs were detected on spinal cord neurons within 24 hr after they were placed in culture, however, and the level of 125I-SP binding increased for several days. SPRs were assayed on spinal motoneurons that had been identified by retrograde labeling with a fluorescent tracer, isolated in high purity by fluorescence-activated cell sorting (FACS), and maintained in culture. Motoneurons grown in isolation from other neurons developed SPRs in vitro along the same time course as neurons in heterogeneous spinal cord cultures. These results show that rat spinal motoneurons can express SPRs early in their development, and they suggest that the initial expression of SPRs by developing motoneurons does not require interaction with other neurons.

Activity of peptide and non-peptide antagonists at peripheral NK1 receptors

We investigated the affinity of several tachykinin antagonists reportedly selective for NK1 receptors at various tachykinin receptors and NK2 receptors subtypes. The four antagonists tested were: L 668,169, Spantide II, Ac-Thr-DTrp(for)-Phe-NMeBzl (FR 113680) and the novel nonpeptide antagonist (+/-)-CP-96,345. The four antagonists were found to be effective against NK1 receptor-mediated responses in the guinea-pig ileum with the following rank order of potency (pKB values in parentheses): (+/-)-CP-96,345 (8.11) greater than Spantide II (7.08) greater than FR 113680 (6.61) greater than or equal to L 558,169 (6.44). (+/-)-CP-96,345, Spantide II and FR 113680 were distinctly more potent at NK1 receptors than at NK2 receptors (NK2A in the rabbit pulmonary artery, NK2B in the hamster trachea). L 668,169 antagonized neurokinin A-induced contractions in the hamster trachea with an affinity similar (pKB value 6.16) to that found in the guinea-pig ileum for NK1 receptors (pKB value 6.44). All antagonists were inactive at NK3 receptors of the rat portal vein. In a second series of experiments, the affinities of test antagonists for NK1 receptors in the guinea-pig ileum were compared to those for NK1 receptors in the guinea-pig vas deferens, the rabbit jugular vein and the rat urinary bladder. For each antagonist, the affinity measured in the guinea-pig vas deferens and the rabbit jugular vein was comparable to that found in the guinea-pig ileum. In the rat urinary bladder, (+/-)-CP-96,345 was about 100 times less potent in blocking NK1 receptor-mediated contractions than in the guinea-pig ileum.(ABSTRACT TRUNCATED AT 250 WORDS)