The Q-soluble N-Ethylmaleimide-sensitive Factor Attachment Protein Receptor (Q-SNARE) SNAP-47 Regulates Trafficking of Selected Vesicle-associated Membrane Proteins (VAMPs)

SNAREs constitute the core machinery of intracellular membrane fusion, but vesicular SNAREs localize to specific compartments via largely unknown mechanisms. Here, we identified an interaction between VAMP7 and SNAP-47 using a proteomics approach. We found that SNAP-47 mainly localized to cytoplasm, the endoplasmic reticulum (ER), and ERGIC and could also shuttle between the cytoplasm and the nucleus. SNAP-47 preferentially interacted with the trans-Golgi network VAMP4 and post-Golgi VAMP7 and -8. SNAP-47 also interacted with ER and Golgi syntaxin 5 and with syntaxin 1 in the absence of Munc18a, when syntaxin 1 is retained in the ER. A C-terminally truncated SNAP-47 was impaired in interaction with VAMPs and affected their subcellular distribution. SNAP-47 silencing further shifted the subcellular localization of VAMP4 from the Golgi apparatus to the ER. WT and mutant SNAP-47 overexpression impaired VAMP7 exocytic activity. We conclude that SNAP-47 plays a role in the proper localization and function of a subset of VAMPs likely via regulation of their transport through the early secretory pathway.

The striatonigral substance P pathway and dopaminergic mechanisms

The biosynthesis of 35S-labelled substance P (SP) has been shown in the rat striatum after continuous delivery of [35S]methionine through a push-pull cannula. In vitro and in vivo studies of SP release have demonstrated that release of the peptide depends on nerve activity and is regulated by presynaptic influences. When the 125I-labelled Bolton and Hunter SP derivative was used, specific binding was observed on mesencephalic cells of the mouse embryo in primary cultures and various characteristics of SP receptors could be determined. Finally, the effects of facilitation or prevention of SP transmission in the substantia nigra on the activity of nigrostriatal dopaminergic neurons have been studied in vivo in the cat by measuring dopamine released from nerve terminals and dendrites. The results obtained indicate that the striatonigral SP neurons exert a tonic facilitatory influence on the dopaminergic neurons.

A 25 year adventure in the field of tachykinins

Several aspects of our 25 year adventure in the field of tachykinins will be successively described. They concern: substance P (SP) synthesis and release in the basal ganglia, the identification and pharmacological characterization of central tachykinin NK(1), NK(2) and NK(3) binding sites and their topographical distribution, the description of some new biological tests for corresponding receptors, the identification of tachykinin NK(1) receptor subtypes or conformers sensitive to all endogenous tachykinins (substance P, neurokinin A (NKA), neurokinin B (NKB), neuropeptide gamma (NP gamma) and neuropeptide K (NPK)) and finally, the functional involvement of these receptors and their subtypes in tachykinin-induced regulations of dopamine and acetylcholine release in the striatum.

The new neurokinin 1-sensitive receptor mediates the facilitation by endogenous tachykinins of the NMDA-evoked release of acetylcholine after suppression of dopaminergic transmission in the matrix of the rat striatum

Using an in vitro microsuperfusion procedure, the NMDA-evoked release of [3H]ACh was studied after suppression of dopamine (DA) transmission (alpha-methyl-p-tyrosine) in striatal compartments of the rat. The effects of tachykinin neurokinin 1 (NK1) receptor antagonists and the ability of appropriate agonists to counteract the antagonist responses were investigated to determine whether tachykinin NK1 classic, septide-sensitive and/or new NK1-sensitive receptors mediate these regulations. The NK1 antagonists, SR140333, SSR240600, GR205171 but not GR82334 and RP67580 (0.1 and 1 microM) markedly reduced the NMDA (1 mm + D-serine 10 microM)-evoked release of [3H]ACh only in the matrix. These responses unchanged by coapplication with NMDA of NK2 or NK3 agonists, [Lys5,MeLeu9,Nle10]NKA(4-10) or senktide, respectively, were completely counteracted by the selective NK1 agonist, [Pro9]substance P but also by neurokinin A and neuropeptide K (1 nM each). According to the rank order of potency of agonists for counteracting the antagonist responses ([Pro9]substance P, 0.013 nM > neurokinin A, 0.15 nM >> substance P(6-11) 7.7 nM = septide 8.7 nM), the new NK1-sensitive receptors mediate the facilitation by endogenous tachykinins of the NMDA-evoked release of ACh in the matrix, after suppression of DA transmission. Solely the NK1 antagonists having a high affinity for these receptors could be used as indirect anti-cholinergic agents.

Presence of NK2 binding sites in the rat brain

Attempts were made to label tachykinin NK2 binding sites in the adult rat brain using [125I]neurokinin A (NKA) as ligand in the presence of NK1 and NK3 agonist or antagonist to avoid labelling of NK1 and NK3 binding sites, respectively. A high-affinity, specifically NK2-sensitive, [125I]NKA-binding, temperature-dependent, reversible, sensitive to GTPgammaS and correspondence to a single population of binding sites (K(D) and B(max) values: 2.2 nM and 7.3 fmol/mg protein) was demonstrated on hippocampal membranes. Competition studies performed with tachykinins and tachykinin-related compounds indicated that the pharmacological properties of these NK2-sensitive [125I]NKA binding sites were identical to those identified in the rat urinary bladder and duodenum. NKA, neuropeptide K, and neuropeptide gamma, as well as the potent and selective NK2 antagonists SR 144190, SR 48968 and MEN 10627, presented a nanomolar affinity for these sites. The regional distribution of these NK2-sensitive [125I]NKA binding sites differs markedly from those of NK1 and NK3 binding sites, with the largest labeling being found in the hippocampus, the thalamus and the septum. Binding in other brain structures was low or negligible. A preliminary autoradiographic analysis confirmed [125I]NKA selective binding in hippocampal CA1 and CA3 areas, particularly, and in several thalamic nuclei.

Different subtypes of tachykinin NK(1) receptor binding sites are present in the rat brain

(2-[(125)I]iodohistidyl(1))Neurokinin A ([(125)I]NKA), which labels "septide-sensitive" but not classic NK(1) binding sites in peripheral tissues, was used to determine whether septide-sensitive binding sites are also present in the rat brain. Binding studies were performed in the presence of SR 48968 (NK(2) antagonist) and senktide (NK(3) agonist) because [(125)I]NKA also labels peripheral NK(2) binding sites and, as shown in this study, central NK(3) binding sites. [(125)I]NKA was found to label not only septide-sensitive binding sites but also a new subtype of NK(1) binding site distinct from classic NK(1) binding sites. Both subtypes of [(125)I]NKA binding sites were sensitive to tachykinin NK(1) antagonists and agonists but also to the endogenous tachykinins NKA, neuropeptide K (NPK), and neuropeptide gamma (NPgamma). However, compounds of the septide family such as substance P(6-11) [SP(6-11)] and propionyl-[Met(O(2))(11)]SP(7-11) and some NK(1) antagonists, GR 82334, RP 67580, and CP 96345, had a much lower affinity for the new NK(1)-sensitive sites than for the septide-sensitive sites. The hypothalamus and colliculi possess only this new subtype of NK(1) site, whereas both types of [(125)I]NKA binding sites were found in the amygdala and some other brain structures. These results not only explain the central effects of septide or SP(6-11), but also those of NKA, NPK, and NPgamma, which can be selectively blocked by NK(1) receptor antagonists.

Further evidence for the presence of "septide-sensitive" tachykinin binding sites in tissues possessing solely NK(1) tachykinin receptors

Binding experiments performed with [(125)I]-NKA allowed us to demonstrate the presence of "septide-sensitive" specific binding sites on membranes from rat CHO cells transfected with the NK(1) receptor cDNA (CHO-rat-NK1 cells), human astrocytoma U373 MG, or mouse cortical astrocytes, cells which express NK(1) but neither NK(2) nor NK(3) receptors. In all cases, [(125)I]-NKA was specifically bound with high affinity (2 to 5 nM) to a single population of sites. In the three preparations, pharmacological characteristics of [(125)I]-NKA binding sites were notably different from those of classical NK(1) binding sites selectively labelled with [(125)I]-BHSP. Indeed, the endogenous tachykinins NKA, NPK, and NKB and the septide-like compounds such as septide, SP(6-11), ALIE-124, [Apa(9-10)]SP, or [Lys(5)]NKA(4-10) had a much higher affinity for [(125)I]-NKA than [(125)I]-BHSP binding sites. Interestingly, differences were also found in the ratio of B(max) values for [(125)I]-NKA and [(125)I]-BHSP specific bindings from one tissue to another. These latter observations suggest that these two types of NK(1) binding sites are present on distinct NK(1) receptor isoforms (or conformers). Finally, while several tachykinins and tachykinin-related compounds stimulated cAMP formation or increased inositol phosphate accumulation in CHO-rat-NK1 cells, these compounds only increased the accumulation of inositol phosphates in the two other preparations.

Pharmacological characterization of tachykinin septide-sensitive binding sites in the rat submaxillary gland

Binding studies have shown that [125I]NKA is a selective ligand of tachykinin septide-sensitive binding sites from membranes of the rat submaxillary gland. Indeed, this ligand bound with high affinity to a single population of sites. In addition, competition studies indicated that natural tachykinins and tachykinin-related compounds had a similar affinity for these sites than for those labeled with [3H]ALIE-124, a selective ligand of septide-sensitive binding sites. Moreover, selective tachykinin NK2, or NK3 agonists or antagonists exhibited weak or no affinity for [125I]NKA binding sites. As indicated by Ki values of several compounds, the pharmacological characteristics of the septide-sensitive binding sites (labeled with [125I]NKA) largely differ from those of classic NK1 binding sites, as determined on crude synaptosomes from the rat brain using [125I]Bolton-Hunter substance P (SP) as ligand. Indeed, several tachykinins including neurokinin A (NKA), neuropeptide K (NPK), neuropeptide gamma (NKgamma), and neurokinin B, as well as some SP and NKA analogues or C-terminal fragments such as septide, ALIE-124, SP(6-11), NKA(4-10), which have a weak affinity for classic tachykinin NK1 binding sites exhibited a high affinity for the septide-sensitive binding sites. In contrast, SP, classic selective NK1 agonists, and antagonists had a high affinity for both types of binding sites. The presence of a large population of tachykinin septide-sensitive binding sites in the rat submaxillary gland may thus explain why NPK and NPgamma induce salivary secretion and may potentiate the SP-evoked response in spite of the absence of tachykinin NK2 receptors in this tissue.

Functional coupling of the NK1 tachykinin receptor to phospholipase D in chinese hamster ovary cells and astrocytoma cells

In [3H]myristic acid-prelabeled Chinese hamster ovary cells stably expressing the rat NK1 tachykinin receptor, the selective NK1 agonist [Pro9]substance P ([Pro9]SP) time and concentration dependently stimulated the formation of [3H]phosphatidylethanol in the presence of ethanol. This [Pro9]SP-induced activation of phospholipase D (PLD) was blocked by NK1 receptor antagonists and poorly or not mimicked by NK2 and NK3 agonists, respectively. In confirmation of previous observations, [Pro9]SP also stimulated the hydrolysis of phosphoinositides, the release of arachidonic acid, and the formation of cyclic AMP (cAMP). All these [Pro9]SP-evoked responses could be mimicked by aluminum fluoride, but they remained unaffected in cells pretreated with pertussis toxin, suggesting that a Gi/Go protein is not involved in these different signaling pathways. The activation of PLD by [Pro9]SP was sensitive to external calcium and required an active protein kinase C because the inhibition of this kinase (Ro 31-8220) or its down-regulation (long-term treatment with a phorbol ester) abolished the response. In contrast, a cAMP-dependent process was not involved in the activation of PLD because the [Pro9]SP-evoked response was neither affected by Rp-8-bromoadenosine 3',5'-cyclic monophosphorothioate nor mimicked by cAMP-generating compounds (cholera toxin or forskolin) or by 8-bromo-cyclic AMP. A functional coupling of NK1 receptors to PLD was also demonstrated in the human astrocytoma cell line U 373 MG stimulated by SP or [Pro9]SP. These results suggest that PLD activation could be an additional signaling pathway involved in the mechanism of action of SP in target cells expressing NK1 receptors.

High affinity binding of [3H]propionyl-[Met(O2)11]substance P(7-11), a tritiated septide-like peptide, in Chinese hamster ovary cells expressing human neurokinin-1 receptors and in rat submandibular glands

Propionyl-[Met(O2)11]substance P(7-11) [ALIE-124 or propionyl-[Met(O2)11]SP(7-11)] has been designed as a septide-like ligand adequate for tritiation and, therefore, adequate for binding studies. In Chinese hamster ovary (CHO) cells expressing human tachykinin neurokinin (NK)-1 receptors, ALIE-124 displaced [3H][Pro9]substance P (SP) from its binding site at micromolar concentrations. However, ALIE-124 stimulated phosphatidylinositol hydrolysis, as previously shown for septide-like peptides. With [3H]ALIE-124 (95 Ci/mmol), we have been able to reveal a high affinity binding site in CHO cells (Kd = 6.6 +/- 1.0 nM), with a low maximal binding capacity. [3H]ALIE-124 specific maximal binding represented only 15-20% of that observed with [3H][Pro9]SP in CHO cells. Septide-like peptides, including septide and NKA, were potent competitors (in the nanomolar range) of [3H]ALIE-124 specific binding site. Interestingly, SP and [Pro9]SP were also potent competitors, with 10-fold greater potency for sites labeled with [3H]ALIE-124 than for sites labeled with [3H][Pro9]SP. The NK-1 antagonist RP 67580 also showed a higher potency for [3H]ALIE-124 than for [3H][Pro9]SP-specific binding sites. NKB and [Lys5,methyl-Leu9,Nle10]NKA(4-10) displaced [3H]ALIE-124 binding but with lower potency, whereas senktide had no affinity. The existence of [3H]ALIE-124 specific binding sites was also demonstrated in rat submandibular gland. In this tissue, [3H]ALIE-124 specific maximal binding was higher, reaching 40-50% of that achieved with [3H][Pro9]SP.

Substance P(6-11) and natural tachykinins interact with septide-sensitive tachykinin receptors coupled to a phospholipase C in the rat urinary bladder

The rat urinary bladder possesses NK1, NK2 (but not NK3) and 'septide-sensitive' tachykinin receptors coupled to a phospholipase C. The present study performed with SR48968 (10(-6) M) to avoid any interaction of the tested peptides with NK2 receptors, indicates that substance P(6-11) (with a high potency), neurokinin A, neurokinin B and to a lesser extent neuropeptide K (with a lower potency) stimulate [3H]-inositol monophosphate ([3H]-IP1) formation in this tissue by acting on the 'septide-sensitive' tachykinin receptors. Substance P(6-11) had little affinity for NK1 binding sites and stimulated [3H]-IP1 formation with an EC50 value and a maximal amplitude similar to those of septide. As previously observed with septide, this maximal response of substance P(6-11) (insensitive to 10(-6) M SR48968) which was about three-fold that of substance P, was blocked by the NK1 receptor antagonist RP67580 and prevented by [Pro9]substance P (NK1 receptor agonist). Similarly, substance P and several substance P C-terminal fragments prevented the substance P(6-11)-evoked response. In addition, neurokinin A, neuropeptide K and neurokinin B induced SR48968-resistant responses which exhibited a maximal amplitude similar to that of substance P (6-11) and were blocked by RP67580 and totally or partially (neuropeptide K) prevented by [Pro9]substance P.

Potency and selectivity of the tachykinin NK3 receptor antagonist SR 142801

Binding studies indicated that tachykinin NK3 binding sites in peripheral (ileum) and central (cerebral cortex) tissues of the guinea pig exhibit similar pharmacological properties. They also confirmed that the tachykinin NK3 receptor antagonist (S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl) propyl)-4-phenylpiperidin-4-yl)-N-methylacetamide (SR 142801) has a higher affinity for tachykinin NK3 binding sites in the guinea pig than in the rat. SR 142801 exhibited a much lower affinity for tachykinin NK2 and NK1 binding sites. SR 142801 was shown to be a potent uncompetitive antagonist of the senktide-induced formation of [3H]inositol monophosphate in slices from the guinea-pig ileum (apparent KB = 3.2 nM, 51% reduction of the maximal response), a functional test for tachykinin NK3 receptors. In agreement with results of binding studies, the effect of SR 142801 was stereoselective since its enantiomer SR 142806 was much less potent. In the rat urinary bladder, a tissue devoid of tachykinin NK3 receptors, SR 142801 was without effect on the [Pro9]substance P- or the septide-induced formation of [3H]inositol monophosphate but it slightly reduced the response of the tachykinin NK2 receptor agonist [Lys5,MeLeu9,Nle10]neurokinin A-(4-10) (KB = 339 nM). Altogether, these data indicate that SR 142801 is a highly selective tachykinin NK3 receptor antagonist which is more potent in the guinea pig than in the rat.

Involvement of septide-sensitive tachykinin receptors in inositol phospholipid hydrolysis in the rat urinary bladder

The selective NK2 agonist [Lys5-MeLeu9,Nle10]NKA(4-10) markedly stimulated [3H]inositol monophosphate (PI1) formation in prisms from the rat urinary bladder. This response was blocked by the NK2 antagonist SR 48968. Senktide (NK3 agonist) was inactive. Septide, a short SP analogue, and the NK1 agonists [Pro9]SP and [Sar9,Met(O2)11]SP also stimulated [3H]IP1 formation and several NK1 tachykinin antagonists (RP 67580, CP 96345, GR 82334, and [D-Pro9,t beta-BPr10,Trp11]SP) were more potent in blocking the septide than the [Pro9]SP response. GR 82334 was the most discriminative. SR 48968 (10(-6) M shifted the [Pro9]SP dose-response curve but did not modify the septide dose-response curve. Septide had a low affinity for [3H][Pro9]SP binding sites, suggesting further that septide and NK1 agonists act on different receptors. Finally, both [Pro9]SP and [Sar9,Met(O2)11]SP blocked the septide-evoked response, acting as partial agonists at the septide-sensitive tachykinin receptors.

Design and synthesis of side-chain conformationally restricted phenylalanines and their use for structure-activity studies on tachykinin NK-1 receptor

Constrained analogues of phenylalanine have been conceptually designed for analyzing the binding pockets of Phe7 (S7) and Phe8 (S8), two aromatic residues important for the pharmacological properties of SP, i.e., L-tetrahydroisoquinoleic acid, L-diphenylalanine, L-9-fluorenylglycine (Flg), 2-indanylglycine, the diastereomers of L-1-indanylglycine (Ing) and L-1-benz[f]indanylglycine (Bfi), and the Z and E isomers of dehydrophenylalanine (delta ZPhe, delta EPhe). Binding studies were performed with appropriate ligands and tissue preparations allowing the discrimination of the three tachykinin binding sites, NK-1, NK-2, and NK-3. The potencies of these agonists were evaluated in the guinea pig ileum bioassay. According to the binding data, we can conclude that the S7 subsite is small, only the gauche (-) probe [(2S,3S)-Ing7]SP presents a high affinity for specific NK-1 binding sites. Surprisingly, the [delta EPhe7]SP analogue, which projects the aromatic ring toward the trans orientation, is over 40-fold more potent than the Z isomer, [delta ZPhe7]SP. A plausible explanation of these conflictual results is that either the binding protein quenches the minor trans rotamer of [(2S,3S)-Ing7]SP in solution or this constrained amino acid side chain rotates when inserted in the protein. In position 8, the high binding affinities of [Flg8]SP and [(2S,3S)-Bfi8]SP suggest that the S8 subsite is large enough to accept two aromatic rings in the gauche (-) and one aromatic ring in the trans direction. Peptides bearing two conformational probes in positions 7, 8, or 9 led to postulate that S7, S8, and S9 subsites are independent from each other. The volumes available for side chains 7 and 8 can be estimated to be close to 110 and 240 A3, respectively. The large volume of the S8 subsite raises question on the localization of the SP-binding site in the NK-1 receptor. If SP were to bind in the transmembrane domains, the cleft defined by the seven transmembrane segments must rearrange during the binding process in order to bind a peptide in an alpha-helical structure and at least one large binding subsite in position 8. Thus, indirect topographical analysis with constrained amino acids might contribute to the analysis of the receptor/ligand dynamics. Finally, this study demonstrates that a good knowledge of the peptidic backbone structure and a combination of constrained amino acids are prerequisites to confidently attribute the preferred orientation(s) of an amino acid side chain.

Differential localization of 3H-[Pro9]SP binding sites in the guinea pig and rat brain

Due to the existence of differences in the pharmacological properties of tachykinin NK-1 receptors in the rat and the guinea pig, the autoradiographic distribution of NK-1 binding sites was compared in the brain of the two species using the selective NK-1 ligand 3H-[Pro9]SP. If a good similarity in the distribution of NK-1 binding sites could be seen in basal ganglia, a relative absence of correlation was observed between the estimated optical densities in other brain structures of the two species. For instance, the interpeduncular nucleus, the lateral habenular nucleus and the deep layers of the cerebral cortex were labeled in the guinea pig but not in the rat while the reverse was observed for the columns of the vermis lobules 9-10, the dorsal raphe nucleus, the medial habenular nucleus, the superficial cortical layers and the dorsal hippocampus. Furthermore, the high similarity found in the localization of 125I-BHSP (a non selective ligand) and 3H-[Pro9]SP binding sites, does not suggest the existence of NK-1 binding site subtypes in the guinea pig brain.

A new selective bioassay for tachykinin NK3 receptors based on inositol monophosphate accumulation in the guinea pig ileum

The selective agonists of tachykinin NK1, NK2 and NK3 receptors, respectively [Pro9]substance P, [Lys5,MeLeu9,Nle10]neurokinin A-(4-10) and senktide, stimulated phosphoinositide breakdown in slices of the guinea pig ileum. This was also the case with septide which has recently been found to act on a new type of tachykinin receptors in this tissue. The NK1, NK2 and septide-evoked responses were completely antagonized in the combined presence of (+/-)-CP-96,345 and MEN 10,376 which are potent and selective antagonists of tachykinin NK1 and NK2 receptors respectively in the guinea pig ileum. Like senktide, other available NK3 receptor agonists, such as [MePhe7]neurokinin B, [MeVal7]neurokinin B, [Pro7]neurokinin B and DiMe-C7, stimulated phosphoinositide hydrolysis in either the absence or combined presence of (+/-)-CP-96,345 and MEN 10,376, although senktide was the most potent. Therefore, following the blockade of tachykinin NK1, NK2 and septide-sensitive receptors, the accumulation of inositol monophosphate appears to be a valuable, rapid and sensitive bioassay for determining the activity of NK3 receptor agonists and putative NK3 receptor antagonists.

NK-1 tachykinin receptor in rat and guinea pig brains: pharmacological and autoradiographical evidence for a species difference

The affinities of a large variety of peptide or nonpeptide tachykinin analogues were determined on membranes from rat and guinea pig brains using the selective NK-1 radioligand 3H-[Pro9]SP. Nonpeptide antagonists clearly revealed a species difference; (+/-)CP-96,345 was more potent in the guinea pig, while RP 67580 was found to be a better competitor of 3H-[Pro9]SP binding to rat brain membranes. This was confirmed on brain slices by autoradiography. Numerous brain structures were analyzed by optical densitometry. From these data, a heterogeneity of NK-1 binding sites among different structures can be excluded in both rat and guinea pig brains.

Higher potency of RP 67580, in the mouse and the rat compared with other nonpeptide and peptide tachykinin NK1 antagonists

1. This study was undertaken to compare the potency and selectivity of the nonpeptide (RP 67580, (+/-)-CP-96,345 and its chloro-derivative [(+/-)-cis-3-(2-chlorobenzylamino)-2-benzhydrylquinuclidine] (CP-C1)) and peptide (GR 71,251 and spantide) neurokinin1 (NK1) antagonists in mouse and rat preparations. 2. Among the NK1 antagonists tested, RP 67580 was the most potent in inhibiting the specific binding of [125I]-Bolton Hunter substance P ([125I]-BHSP) to crude synaptosomes from the rat brain (Ki: 2.9 nM). (+/-)-CP-96,345 was about ten fold less potent (Ki: 31 nM) than RP 67580 while other compounds exhibited even less affinity. 3. All NK1 antagonists inhibit competitively the activation of phospholipase C by [Pro9]substance P ([Pro9]SP) in cultured cortical astrocytes from the newborn mouse, a preparation rich in NK1 receptors but devoid of NK2 and NK3 receptors. pA2 values for the most potent compounds, RP 67580 and (+/-)-CP-96,345, were 8.28 and 7.08 respectively. When used alone, all antagonists showed some agonist activity at 10(-5) M, except spantide which was already effective at 10(-6) M. 4. An excellent correlation was found between the potency of the NK1 antagonists in blocking the stimulation by [Pro9]SP of phosphoinositide breakdown in cortical astrocytes and in inhibiting [125I]-BHSP specific binding to rat brain synaptosomes. 5. As shown on single cells by use of the Indo-1 microfluorometric method, RP 67580 (10(-7) M) prevented reversibly the elevation of cytosolic calcium concentration induced by [Pro9]SP (10(-8) M) in cultured cortical astrocytes. 6. Several experiments indicated that the antagonists were highly selective for NK1 receptors. RP 67580 did not modify the noradrenaline-evoked activation of phospholipase C in cortical astrocytes; when used at 10-5 M all antagonists had no or only little affinity for NK2 or NK3 binding sites and did not block the NKA (10-8 M)-induced activation of phospholipase C in the hamster urinary bladder (a selectiveNK2 test).7. In conclusion, RP 67580 appears to be a potent NK1 antagonist in the mouse and the rat. Results obtained with (+/-)-CP-96,345 confirm the lower potency of this compound in these two species when compared with reported data obtained in the guinea-pig or man.

The nonpeptide NK-2 antagonist SR 48968 is also a NK-3 antagonist in the guinea but not in the rat

SR 48968 was first described as a NK-2 nonpeptide receptor antagonist; we report here that SR 48968 interacts also with guinea pig but not rat NK-3 cortical binding sites. Furthermore, SR 48968 is shown to inhibit the senktide- (a NK-3 selective agonist) evoked stimulation of phosphoinositide turnover in guinea pig ileum slices. The species difference observed for the NK-3 receptor with SR 48968 was confirmed by the determination of the affinities of NK-3 peptide agonists. [Pro7]neurokinin B particularly was found to have a greater affinity for cortical NK-3 binding sites in the rat than in the guinea pig.

[Pro9]SP and [pGlu6, Pro9]SP(6-11) interact with two different receptors in the guinea-pig ileum as demonstrated with new SP antagonists

Structural considerations led us to postulate that the introduction of the dipeptides DPro9-Pro10 and DPro9-MeLeu10 should lock the C-terminal tetrapeptide of SP in a type II' beta-turn structure, a prerequisite for antagonist activity. Indeed, as the GR 71251, [DPro9, Pro10, Trp11]SP was more potent in inhibiting the septide, (pA2 = 6.5), than the [Pro9]SP, (pA2 < or = 5), spasmogenic activity in the guinea-pig ileum bioassay. This result confirms that septide, [pGlu6, Pro9]SP(6-11), a peptide active in the guinea-pig ileum bioassay and practically devoid of binding potencies for the three specific NK-1, NK-2 and NK-3 tachykinin binding sites interacts with a tachykinin receptor different from the NK-1 receptor sensitive to [Pro9]SP. Interestingly enough, the reintroduction of the leucine side-chain in position 10 yielded [DPro9, MeLeu10, Trp11]SP, an antagonist, equipotent in inhibiting both the septide- and the [Pro9]SP-evoked contractile response in the guinea-pig ileum bioassay, (pA2 = 6.6).

[A new tachykinin receptor revealed by substance P analogues in the guinea pig ileum]

[Pro9]SP and septide have been described as selective agonists for the SP receptor (NK-1 type). These two peptides contract with a great efficacy the guinea-pig ileum, but unexpectedly septide was practically devoid of affinity for the NK-1 site labelled by 3H-[Pro9]SP. Like septide, SP analogues like SP-O-CH3, [Apa9-10]SP and [Pro9,10]SP share the same peculiar properties. In addition, the contracting activity of these peptides is not explained by an interaction with NK-2 or NK-3 sites. GR 71,251, a compound which has been described as NK-1 antagonist, was more potent in inhibiting the septide- and the [Apa9-10]SP- than the [Pro9]SP-evoked contracting responses. Altogether, these results suggest that septide, SP-O-CH3, [Apa9-10]SP and [Pro9,10]SP exert their high contracting activity in the guinea-pig ileum by acting on a new type of tachykinin receptor.

Possible existence of a new tachykinin receptor subtype in the guinea pig ileum

The guinea pig ileum possesses NK-1 and NK-3 tachykinin receptors. As expected, [Pro9]SP and senktide, which are selective agonists of NK-1 and NK-3 receptors, respectively, were found to be highly potent in contracting the guinea pig ileum. Surprisingly, similar observations were made with septide, SP-O-CH3, [Apa9-10]SP, or [Pro9,10]SP although, in contrast to [Pro9]SP, these four peptides showed a low affinity for 3H-[Pro9]SP-specific NK-1 binding sites on membranes from the guinea pig ileum. They were also devoid of affinity for NK-2 and NK-3 binding sites. GR 71251, a compound which has been described as a NK-1 antagonist, was more potent in inhibiting the septide- than the [Pro9]SP-evoked contracting response. Altogether, these results suggest that septide, [Apa9-10]SP, and [Pro9,10]SP exert their high contracting activity in the guinea pig ileum by acting on a new subtype of tachykinin receptors.

Inhibitory effects of substance P and carbachol on the saturable sodium-dependent uptake process of myo-inositol in rat parotid gland

myo-Inositol uptake in prisms of rat parotid glands was investigated by measuring both the accumulation of free myo-[3H] inositol into the cytosol and its incorporation into phospholipids. Total myo-[3H]inositol uptake involved two distinct processes, a prominent one which is saturable and sodium-dependent (Km, 95 microM; Vmax, 8 pmol/mg of protein per min) and a minor one, nonsaturable and sodium-independent. Phloretin and cytochalasin B, two inhibitors of hexose transport, and D-glucose, but only at high concentrations (greater than 10 mM), inhibited myo-[3H]inositol uptake. Dixon plots of the data indicated that D-glucose inhibition was noncompetitive suggesting that myo-inositol and D-glucose are transported by different carriers. Electrogenic cotransport of sodium and myo-inositol, rather than energy derived from mitochondrial oxidative metabolism, seems to be involved in the transport process. Thus, ouabain, monensin or veratridine, all of which increase intracellular sodium concentrations, reduced myo-[3H]inositol uptake, whereas dinitrophenol, potassium cyanide and carbonyl cyanide m-chlorophenyl hydrazone were without effect. Substance P affected only the sodium-dependent uptake process of myo-[3H]inositol, this inhibitory effect requiring extracellular calcium. Similar observations were made with the muscarinic agonist carbachol. From these results, an increase in intracellular sodium concentration linked to the activation of calcium-sensitive cation-permeant channels appears to be responsible for the inhibitory effects of substance P and carbachol on myo-[3H]inositol uptake, these effects being mediated respectively by NK1 and muscarinic receptors coupled to a phospholipase C.

Influence of the replacement of amino acid by its D-enantiomer in the sequence of substance P. 1. Binding and pharmacological data

The D-enantiomer of residues 2, 4, 5, 6, 7, 8, 10 and 11 was introduced in the sequence of Substance P: Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2. The achiral glycine residue was replaced by a D-Ala residue. Regarding NK-1 binding potencies or activities, changing to the D-enantiomer in positions 2, 4 or 5 did not modify the pharmacological patterns of the resulting peptides. Introduction of a D-residue in the 6 to 11 sequence drastically decreased the potency of the D-analogues with the exception of [D-Leu10]SP which was found only three times less potent than SP in contracting the guinea-pig ileum. No clear cut evidence between the binding potencies and activities on NK-1, NK-2 and NK-3 assays, was observed which allows a more rational design of tachykinins antagonists.

NK-1 receptors are the only class of tachykinin receptors found on mouse cortical astrocytes

Extending our previous studies, our results indicate that cultured cortical astrocytes from the mouse possess only NK-1 receptors coupled to phospholipase C. An excellent correlation was found in the potency of tachykinins and selective analogs at inhibiting 125I-BHSP binding and at stimulating phospholipase C activity, their rank order being that of NK-1 receptors. No binding sites could be found with ligands of NK-2 or NK-3 receptors. No additive effect could be shown with NK-2 or NK-3 agonists when phospholipase C activity was estimated with high concentrations of NK-1 agonists. C- or N-terminal SP fragments did not modify SP- or [Pro9]SP-evoked responses.

Selective agonists of NK-2 binding sites highly active on rat portal vein (NK-3 bioassay)

All the synthetized NKA and NKA (4-10) agonists have been found active in the rat portal vein bioassay. Even [Lys5, MeLeu9, Nle10] NKA(4-10), a highly potent competitor of NK-2 binding sites with very low binding potencies for NK-1 and NK-3 sites (IC50 greater than microM) is still active in contracting the rat portal vein. These results suggest that this tissue contains not only a fairly large population of NK-3 receptors but also a minor population of NK-2 receptors. Comparison of the activities of NKA C-terminal analogues on the guinea-pig ileum suggests that 1) only a small population of NK-2 receptors are present in this tissue and 2) beside NK-1, NK-2 and NK-3 receptors, another type of receptor sensitive to C-terminal sequences might be present in the guinea-pig tissue.

Further demonstration that [Pro9]-substance P is a potent and selective ligand of NK-1 tachykinin receptors

Previous studies have indicated that [Pro9]-substance P ([Pro9]-SP) possesses very good affinity for NK-1 binding sites and that, in contrast to substance P, it interacts selectively with these sites. Therefore, [3H][Pro9]-SP (75 Ci/mmol) was synthesized in order to study its binding to membranes of the rat brain. Specific binding of [3H][Pro9]-SP (75% of total binding) was temperature-dependent, saturable, and reversible. Scatchard analysis and Hill plots revealed the existence of a single population of noninteracting binding sites (KD and Bmax values: 1.48 nM and 29.7 fmol/mg of protein, respectively). Competition studies with several tachykinins and analogues indicated that the pharmacological profile of [3H][Pro9]-SP binding sites is identical to that of NK-1 binding sites. Rat brain sections labeled with either [3H][Pro9]-SP or [3H]SP, revealed a close similarity in the topographical distribution of [3H][Pro9]-SP and [3H]SP binding sites. Biochemical, pharmacological, and autoradiographic data obtained with [3H][Pro9]-SP did not provide any evidence for the existence of subtypes of NK-1 binding sites. [Pro9]-SP had neither agonist nor antagonist properties on NK-2 and NK-3 receptors. Indeed, it did not stimulate phosphoinositide turnover on the hamster urinary bladder (NK-2 assay) and was devoid of activity on the contraction of the rabbit pulmonary artery (NK-2 assay) and of the rat portal vein (NK-3 assay). As a result of its high selectivity, [Pro9]-SP thus appears an excellent tool for investigating the functional properties of NK-1 receptors.

Selective agonists of tachykinin binding sites

Three types of binding sites for the mammalian tachykinins, ie Substance P (SP) Neurokinin A (NKA) and Neurokinin B (NKB), have been found in both the central and peripheral nervous systems. Substance P binds to the NK-1 subclass of binding site while NKA and NKB are less selective endogenous ligands, which preferentially interact with the NK-2 and NK-3 subclasses of binding sites, respectively. Complementary strategies, including 3-dimensional structure analysis by NMR spectroscopy and structure-activity relationship led to the design of selective agonists of these binding sites. [Pro9] SP, [Pro10] SP and the cyclic analogues [Cys3,6, Tyr8, Pro9] SP and [Cys3,6, Tyr8, Pro10] SP are selective NK-1 agonists. [Lys5] NKA(4-10) is a water soluble NK-2 potent agonist. Finally, [Pro7] NKB, which completely discriminates NK-2 and NK-3 binding sites, is a water-soluble NK-3 selective agonist.

Marked regional heterogeneity of 125I-Bolton Hunter substance P binding and substance P-induced activation of phospholipase C in astrocyte cultures from the embryonic or newborn rat

The specific binding of 125I-Bolton Hunter substance P (125I-BHSP) was estimated on 4- to 5-week-old primary cultures of astrocytes from several brain structures and the spinal cord of 16-day-old embryonic or newborn rats. In both cases, high levels of binding of 125I-BHSP were found on intact astrocytes from the brainstem, but this binding was low or negligible on cells from the cerebral cortex, striatum, hypothalamus, and mesencephalon. In addition, hippocampal astrocytes from newborn rats were also devoid of 125I-BHSP binding sites, while a binding of 125I-BHSP (half that of brainstem cells) was observed on astrocytes from the cerebellum and spinal cord. It was also shown that this regional heterogeneity in 125I-BHSP binding was not linked to differences in the inactivation of the ligand, cell plating density. or eventual cell contaminants. Five-day-old cultures from 16-day-old embryos were used to estimate 125I-BHSP binding on neuron-enriched cultures. Specific 125I-BHSP binding was found on cells from the brainstem, mesencephalon, and hypothalamus, but neurons from the cerebral cortex or the striatum contained low or negligible amounts of 125I-BHSP binding sites. Competition studies using tachykinins and SP analogues indicated that 125I-BHSP binding sites on brainstem astrocytes (16-day-old embryos) have the pharmacological profile expected for NK1 binding sites. SP (1 microM) stimulated phosphoinositide breakdown in cells rich in 125I-BHSP binding sites (brainstem) but not in those devoid of 125I-BHSP binding (striatum).(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P-induced reduction in the initial accumulation of cytosolic myo-[3H]inositol in rat parotid acinar cells mediated by the NK1 tachykinin receptor

Stimulation of rat parotid acinar cells by the tachykinin neurokinin (NK) 1 receptor agonist substance P (SP) resulted in a significant reduction in the initial accumulation of cytosolic myo-[3H]inositol. This effect was rapid, because a reduction of approximately 15% could be seen already at 30 s. with the maximal effect (approximately 45%) being observed at 15 min. The response to SP stimulation was temperature dependent, because at 4 degrees C no reduction was found. In addition, at 4 degrees C, cytosolic myo-[3H]inositol represented only 10% of the labeled inositol accumulated at 37 degrees C. The SP-induced reduction in cytosolic myo-[3H]inositol accumulation was concentration dependent; the EC50 obtained for SP was 5.8 +/- 2.5 nM. Spantide [D-Arg1, D-Trp7.9, Leu11]SP), a SP antagonist, used at a concentration of 10(-5) M, gave a competitive shift of the dose-response curve to SP. Various tachykinins and their analogs were evaluated for their ability to reduce cytosolic myo-[3H]inositol. [L-Pro9]SP and SP methyl ester, two highly selective agonists of NK1 receptors, reduced the initial accumulation of myo-[3H]inositol with EC50 values of 2.3 and 67.0 nM, respectively. Long SP C-terminal fragments were more potent than shorter ones. SP N-terminal fragments and SP free acid were without effect. [Pro7]NKB, a selective NKB analog, had no effect. The rank order of potency of mammalian tachykinins was SP greater than NKA greater than NKB. These findings and the close correlation between EC50 values and IC50 values obtained in binding studies implicate the NK1 receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Tachykinin receptors of the NK1 type (substance P) coupled positively to phospholipase C on cortical astrocytes from the newborn mouse in primary culture

Specific 125I-Bolton-Hunter substance P (125I-BHSP) binding sites are present on intact cortical astrocytes of the newborn mouse in primary culture. Therefore, these cells were used to ascertain the existence of functional substance P (SP) receptors coupled positively to phospholipase C. SP stimulated phosphoinositide breakdown with an EC50 value (4.5 x 10(-10) M) similar to its IC50 value (3.8 x 10(-10) M) for inhibiting 125I-BHSP binding. The maximal response to (10(-6) M SP for 60 min) obtained was approximately 500% of control values. The rank order of potency of tachykinins was SP greater than neurokinin (NK) A greater than NKB. Long SP C-terminal fragments were more potent than shorter ones in stimulating the accumulation of 3H-inositol phosphates. SP free acid and SP N-terminal fragments were without effect. [L-Pro9]SP and SP methyl ester, two selective agonists of NK1 receptors, were almost as potent as SP. An excellent correlation was found when the abilities of tachykinins and their analogs for stimulating phosphoinositide breakdown and for inhibiting 125I-BHSP binding were compared. Finally, when used at a concentration of 3 x 10(-6) M, spantide [( D-Arg1, D-Trp7,9, Leu11]SP), an SP antagonist, competitively reduced the stimulatory effect of SP on accumulation of 3H-inositol phosphates. These results demonstrate the presence of functional SP receptors (NK1) on cortical astrocytes from the newborn mouse in primary culture.

Tachykinin binding sites in the interpeduncular nucleus of the rat: normal distribution, postnatal development and the effects of lesions

Tachykinin binding sites in the basal midbrain were labeled in adult and neonatal rats using 125I-Bolton Hunter (BH) substance P (SP) and 125I-BH eledoisin as ligands. In the adult, binding was very low in the tegmentum and raphe adjacent to the interpeduncular nucleus (IPN). Within the IPN, no binding with either ligand was seen in the target subnuclei of the habenular SP and substance K projections, the lateral subnuclei and the cap of the rostral subnucleus. Labeling with 125I-BH-SP was very light and was restricted primarily to the central subnucleus of the IPN while 125I-BH-eledoisin labeling was very dense over the dorsal, the ventral sector of the rostral, the intermediate and the central subnuclei. Lesions of major afferents to the IPN, the fasciculus retroflexus or the locus coeruleus, had no effect on the distribution or density of the binding of either ligand. In rats 0, 4 or 7 days or age, 125I-BH-SP binding was very dense in the ventral tegmental region, the raphe and in the dorsal, rostral and central subnuclei. 125I-BH-eledoisin binding was extremely dense in the raphe and in the dorsal, rostral, intermediate and central subnuclei but was less dense in the ventral tegmentum. Adult levels of binding in the midbrain were established by 11 days of age. Neonatal lesions restricted to the fasciculus retroflexus had no effect on the density of labeling with either ligand in animals allowed to reach adulthood.

An isolated growth cone-enriched fraction from developing rat brain has substance P binding sites

A fraction enriched in neuronal growth cones isolated from developing rat forebrain was shown to possess binding sites for the substance P analog, Bolton-Hunter substance P [( 125I]BHSP). Specific binding of this ligand reached an equilibrium after 10 min at 20 degrees C, and was reversible and temperature-dependent. Removal of extracellular Na+ did not block but rather augmented [125I]BHSP binding suggesting that the labeled analog was not transported into the growth cone fraction. Scatchard analysis of the binding indicated a single class of non-interacting binding sites in the growth cone fraction (Kd: 257 pM; Bmax: 56 fmol/mg protein). From competition studies using substance P and other tachykinins, their rank order of potency for inhibiting [125I]BHSP binding was SP greater than physalaemin much greater than eledoisin greater than kassinin greater than NKB greater than or equal to NKA. Such order is consistent with the presence of an SP receptor (Neurokinin-1) in the growth cone fraction. The N-terminal fragments of substance P, SP1-7 and SP1-11 free acids, and the C-terminal fragment, SP7-11, were devoid of affinity for the [125I]BHSP binding site. However SP6-11 and SP1-11 methyl esters showed more potency.

Localization of tachykinin binding sites (NK1, NK2, NK3 ligands) in the rat brain

A comparative autoradiographic analysis of the distribution of tachykinin binding sites was made on brain serial sections using several ligands. (1) 3H-SP, 125I-BHSP and 3H-physalaemin labeled identical binding sites (NK1 type). (2) 3H-NKB, 125I-BHE and 3H-eledoisin also labeled identical sites (NK3 type). (3) 125I-BHNKA preferentially labeled NK3 binding sites, the distribution of 125I-BHNKA binding sites being identical to that of 3H-NKB or 125I-BHE binding sites. (4) The distributions of 3H-SP and 3H-NKB binding sites were markedly different. (5) A very low density of labeling was found with 3H-NKA or 125I-NKA, and these binding sites were distributed only in areas rich in either 3H-SP or 3H-NKB binding sites. (6) Particular efforts were made to look for the presence of tachykinin binding sites in the substantia nigra, since this structure is particularly rich in SP and NKA and contains functional tachykinin receptors of the NK1 and NK2 types as suggested by physiological studies. Confirming previous reports, low or very low labeling was observed in the substantia nigra with 3H-SP or 125I-BHSP and 3H-NKB or 125I-BHE. Similar results were found with 3H-NKA, 125I-NKA or 125I-BHNKA. In conclusion, our data do not provide evidence yet for the existence of NK2 binding sites in the rat brain.

3H-neurokinin A labels a specific tachykinin-binding site in the rat duodenal smooth muscle

3H-Neurokinin A (3H-NKA) with high specific activity (75 Ci/mmol) was synthesized to study NKA (NK-2)-binding sites on membrane preparations of various tissues in the rat, including brain, spinal cord, duodenum, vas deferens, and ileum. The binding capacity of 3H-NKA (0.9 nM) was very low in membrane preparations of different central nervous system regions and the ileum smooth muscle (0.2-2 fmol/mg of protein). In contrast, relatively high specific binding was found in membrane suspensions of the rat duodenal smooth muscle (18 fmol/mg of protein) and the vas deferens (8 fmol/mg of protein). 3H-NKA-binding sites were further characterized on the rat duodenal smooth muscle. The specific binding of 3H-NKA was shown to be temperature dependent, saturable, reversible, and increased in parallel with the protein concentration. Scatchard analyses and Hill plots of equilibrium binding studies in the concentration range of 0.40-30 nM revealed that 3H-NKA bound to a single class of noninteracting binding sites (Bmax = 270 fmol/mg of protein, KD = 13.3 nM). Displacement of 3H-NKA with different tachykinin-related peptides gave the following rank order of potencies: NKA greater than NKA (4-10) greater than kassinin greater than eledoisin greater than NKB much greater than substance P greater than physalaemin, which suggests that the binding site labeled by 3H-NKA is different from substance P (NK-1)-and NKB (NK-3)-binding sites. The biological activities of tachykinins and related peptides were tested by measuring their contractile effects on the rat duodenum and rabbit pulmonary artery, two tissues known to be sensitive for NKA. Ki values were correlated with the EC50 obtained in biological assays. The results revealed a significant correlation (r = 0.86, p less than 0.01) between Ki and EC50 values obtained in the isolated rabbit pulmonary artery, whereas there was no significant correlation between binding affinities and biological responses on the rat duodenum (r = 0.62, p greater than 0.05).

Interaction of tachykinins with their receptors studied with cyclic analogues of substance P and neurokinin B

The activities of two groups of cyclic agonists of substance P (SP) have been studied. The disulfide bridge constraints have been designed on the basis of conformational studies on SP and physalaemin indicating an alpha-helical structure for the core of these two tachykinins (group I) and a folding of the C-terminal carboxamide towards the side chains of the glutamines 5 and 6 (group II). Only peptides simulating the alpha-helix present substantial potencies. [Cys3,6]SP is as active as SP in inhibiting 125I-labeled Bolton and Hunter SP-specific binding on rat brain synaptosomes and on dog carotid bioassay, two assays specific for the neurokinin 1 receptor. Moreover, [Cys3,6]SP is as potent as neurokinin B in inhibiting 125I-labeled Bolton and Hunter eledoisin-specific binding on rat cortical synaptosomes as well as in stimulating rat portal vein, two tests specific for the neurokinin 3 receptor. Interestingly, in contrast to neurokinin B, [Cys3,6]SP is a weak agonist of the neurokinin 2 receptor subtype, as evidenced by its binding potency in inhibiting 3H-labeled neurokinin A-specific binding on rat duodenum and in inducing the contractions of the rabbit pulmonary artery, a neurokinin 2-type bioassay. To increase the specificity of the cyclic analogue [Cys3,6]SP positions 8 and 9 were modified. [Cys3,6, Tyr8, Ala9]SP is slightly less selective than SP for the neurokinin 1 receptor subtype. [Cys2,5]neurokinin B constitutes a selective cyclic agonist for the neurokinin 3 receptor. The very weak potencies of the peptides from group II indicate that a certain degree of flexibility in the C-terminal moiety is required. Collectively, these results suggest that the neurokinin 1 and neurokinin 3 tachykinin receptors may recognize a similar three-dimensional structure of the core of the tachykinins. Different orientations of the common C-terminal tripeptide may be related to the selectivity for the different receptor subtypes.

Sulfhydryl reagents have different effects on substance P and neurokinin B binding sites on cortical synaptosomes in the rat

The effects of several protein modifying reagents, including phenoxybenzamine, N-ethylmaleimide (NEM), 5,5'-dithiobis (2-nitro)--benzoic acid (DTNB), p-chloromercuryphenyl sulfonic acid (PCMP) and p-bromophenacylbromide (PBPB), on the binding of 125I-Bolton Hunter substance P (125I-BHSP), 125I-Bolton Hunter eledoisin (125I-BHELE) and 3H-neurokinin B (3H-NKB)4 to cortical synaptosomes were examined. PCMP (10(-4) M), DTNB (10(-4) M) and NEM (10(-3) M) were without effect on the 125I-BHSP binding but reduced markedly the specific binding of 125I-BHELE or 3H-NKB. Although phenoxybenzamine and PBPB inhibited the 125I-BHSP binding when used in high concentrations (10(-4) M and 10(-3) M), they were more potent in inhibiting the 125I-BHELE or 3H-NKB binding. These results indicate that the NKB binding site is more sensitive to alkylating reagents than the SP binding sites and that these reagents can be used to distinguish SP and NKB receptors in the brain.

[3H]neurokinin B and 125I-Bolton Hunter eledoisin label identical tachykinin binding sites in the rat brain

[3H]Neurokinin B ([3H]NKB) of high specific activity (75 Ci/mmol) was synthesized for study of its binding to crude synaptosomes from the rat cerebral cortex. The specific binding of [3H]NKB (75% of total binding) was temperature dependent, saturable, and reversible. Scatchard analyses and Hill plots showed the existence of a single population of noninteracting binding sites (KD = 4.3 nM; Bmax = 123 fmol/mg of protein). Competition studies indicated the following rank order of potencies among tachykinins: NKB greater than eledoisin (E) greater than kassinin greater than physalaemin greater than neurokinin A (NKA) greater than substance P (SP), a result suggesting that NKB might be the endogenous ligand for [3H]NKB binding sites. It is of interest that 127I-Bolton Hunter (BH) NKA (127I-BHNKA) was much more potent than NKA in inhibiting the specific binding of [3H]NKB, which raises certain questions concerning the use of 125I-BHNKA as a ligand for NKA binding sites in the brain. These results, as well as those obtained with different SP analogues, show a close similarity to those obtained previously with 125I-BHE binding to cortical synaptosomes. This suggested that the two ligands labeled identical binding sites. In addition, using either [3H]NKB or 125I-BHE as ligands, similar displacement curves were obtained with increasing concentrations of NKB and 127I-BHE. The similarity of the [3H]NKB and 125I-BHE binding sites was further confirmed by comparison of their localization on rat brain sections by autoradiography. The distribution of binding sites for [3H]NKB and 125I-BHE was identical throughout the brain, and the highest density of binding sites for the two ligands was found in layers IV and V of the cerebral cortex, the paraventricular nucleus of the hypothalamus (magnocellular part), and the ventral tegmental area.

Substance P receptors in primary cultures of cortical astrocytes from the mouse

Binding sites for substance P were labeled on intact cortical glial cells from newborn mice in primary culture using 125I-labeled Bolton-Hunter-labeled substance P. Maximal specific binding (95% of total binding) was reached after 2-3 weeks in culture. The binding was saturable, reversible, and temperature dependent. Scatchard and Hill analysis revealed a single population of noninteracting high-affinity binding sites (Kd, 0.33 nM; Bmax, 14.4 fmol per dish). Competition studies made with tachykinins and substance P analogues indicated that the characteristics of the 125I-labeled Bolton-Hunter labeled substance P binding sites on glial cells were identical to those on rat brain synaptosomes. 125I-labeled Bolton-Hunter labeled substance P binding sites were visualized by autoradiography, and differences in the intensity of labeling were seen among astrocytes. Substance P was found to stimulate phosphatidylinositol turnover; the EC50 value (0.36 nM) was identical to the IC50 value (0.38 nM) determined in binding studies. 125I-labeled Bolton-Hunter labeled substance P binding sites were also found on astrocytes derived from other brain structures and from the spinal cord of mice.

A cyclic analogue selective for the NKB specific binding site on rat brain synaptosomes

The cyclic analogue of NKB, [Cys2,Cys5]NKB is as active as SP and NKB in the guinea-pig ileum bioassay. Furthermore, [Cys2,Cys5]NKB is a selective substrate for the [3H]NKB specific binding site on rat cortical synaptosomes. Its binding potencies for [3H]NKB and 125I-BHSP binding sites, IC50 = 5.2 nM and 3.4 microM respectively were close to those observed for NKB.

Quantitative autoradiographic analysis of the distribution of binding sites for [125I]Bolton Hunter derivatives of eledoisin and substance P in the rat brain

[125I]Bolton and Hunter eledoisin binds to a single class of non-interacting sites in rat cerebral cortex tissue sections with an apparent Kd of 9.9 nM and a Bmax of 244 fmol/mg protein. When concentrations of up to 23 nM [125I]Bolton and Hunter eledoisin were used, [125I]Bolton and Hunter eledoisin binding was specific, saturable and reversible. Kassinin, eledoisin and neurokinin B were more potent than substance P and neurokinin A in inhibiting the specific binding of [125I]Bolton and Hunter eledoisin to cerebral cortex tissue sections. These kinetic and pharmacological characteristics are consistent with results obtained from binding studies on cortical synaptosomes. When the localization of [125I]Bolton and Hunter substance P and [125I]Bolton and Hunter eledoisin binding sites were compared, differences in many areas of the brain were noted. Large differences were seen in the paraventricular and supraoptic hypothalamic nuclei, and in layers IV and V of the cerebral cortex, which were densely labeled by [125I]Bolton and Hunter eledoisin, but not by [125I]Bolton and Hunter substance P. In contrast, nuclei of the septum (diagonal band of Broca, septohippocampal nucleus, dorsal part of the lateral septal nucleus), the rostrodorsal part of the hippocampus and other discrete nuclei [endopyriform nucleus, anterior cortical amygdaloid nucleus, the vermis columns (9-10), the dorsal tegmental nucleus, the hypoglossal and ambiguus nucleus] had high levels of [125I]Bolton and Hunter substance P binding but were only labeled weakly by [125I]Bolton and Hunter eledoisin. Thus, the two ligands seem to label different sites, since these binding sites have different biochemical and pharmacological properties, and are localized in different anatomical structures.

Pharmacological characterisation of two tachykinin binding sites in the rat cerebral cortex

The pharmacological properties of two types of tachykinin receptor were characterised on rat cortical synaptosomes using 125I-Bolton Hunter substance P (125I-BHSP) or with 125I-Bolton Hunter eledoisin (125I-BHE). Shorter SP C-terminal fragments, such as SP (6-11) or (pGlu)-SP (6-11), were more potent than SP itself or longer SP C-terminal fragments in competing for 125I-BHE binding; their efficacy was comparable to that of eledoisin. In contrast, longer SP C-terminal fragments exhibited a higher affinity than shorter ones for the 125I-BHSP binding sites as previously reported. SP N-terminal fragments were devoid of activity on either type of binding sites. SP methyl ester inhibited 125I-BHSP binding but was without effect on 125I-BHE binding whilst, DiMe-C7, a metabolically stable tachykinin analog, had the opposite selectivity. Eledoisin related peptide (ERP) was less effective than either SP or eledoisin on 125I-BHSP and 125I-BHE binding sites respectively. Finally, the undecapeptide or octapeptide SP antagonists, which are weak inhibitors of 125I-BHSP binding, had negligable activity on 125I-BHE binding sites.