Expression of tachykinin receptors (tacr1a and tacr1b) in zebrafish: influence of cocaine and opioid receptors.

Opioid and tachykinin receptors (TACRs) are closely related in addiction and pain processes. In zebrafish, opioid receptors have been cloned and characterized both biochemically and pharmacologically. However, the tacr1 gene has not yet been described in zebrafish. The aim of this research was to identify the tacr1 gene, study the effects of cocaine on tacr1, and analyze the interaction between tacr1 and opioid receptors. We have identified a duplicate of tacr1 gene in zebrafish, designated as tacr1a and tacr1b. Phylogenetic analyses revealed an alignment of these receptors in the Tacr1 fish cluster, with a clear distinction from other TACR1s of amphibians, birds, and mammals. Our qPCR results showed that tacr1a and tacr1b mRNAs are expressed during embryonic development. Whole-mount in situ hybridization showed tacr1 expression in the CNS and in the peripheral tissues. Cocaine (1.5 µM) induced an upregulation of tacr1a and tacr1b at 24 and 48 h post-fertilization (hpf; except for tacr1a at 48 hpf, which was downregulated). By contrast, HEK-293 cells transfected with tacr1a and tacr1b and exposed to cocaine showed a downregulation of tacr1s. The knockdown of ZfDOR2 and ZfMOR, opioid receptors, induced a down- and upregulation of tacr1a and tacr1b respectively. In conclusion, tacr1a and tacr1b in zebrafish are widely expressed throughout the CNS and peripherally, suggesting a critical role of these tacr1s during embryogenesis. tacr1a and tacr1b mRNA expression is altered by cocaine exposure and by the knockdown of opioid receptors. Thus, zebrafish can provide clues for a better understanding of the relationship between tachykinin and opioid receptors in pain and addiction during embryonic development.

Loperamide inhibits tachykinin NK3-receptor-triggered serotonin release without affecting NK2-receptor-triggered serotonin release from guinea pig colonic mucosa.

The effect of loperamide on tachykinin NK(2)- and NK(3)-receptor-mediated 5-HT outflow from guinea pig colonic mucosa was investigated in vitro. The selective tachykinin NK(2)-receptor agonist [beta-Ala(8)]-neurokinin A(4-10) (betaAla-NKA) or the selective NK(3)-receptor agonist senktide elicited an increase in 5-HT outflow from whole colonic strips, but not from mucosa-free muscle layer preparations. The enhancing effect of betaAla-NKA and senktide was prevented by the selective NK(2)-receptor antagonist GR94800 or the selective NK(3)-receptor antagonist SB222200. Loperamide concentration-dependently suppressed the senktide-evoked 5-HT outflow, but failed to affect the betaAla-NKA-evoked 5-HT outflow. The kappa-opioid receptor antagonist nor-binaltorphimine or the delta-opioid receptor antagonist naltrindole displaced the concentration-response curve for the suppressant action of loperamide to the right without significant depression of the maximum. However, the mu-opioid receptor antagonist CTOP did not affect the suppressant effect of loperamide. We concluded that the NK(3) receptor-triggered 5-HT release from colonic mucosa is suppressed by loperamide-sensitive mechanisms, whereas the NK(2)-receptor-triggered 5-HT release is loperamide-insensitive. Our data also suggest that the suppressant effect of loperamide is probably mediated by the activation of kappa- and delta-opioid receptors located on intrinsic neurons.

Tachykinins and tachykinin receptors: a growing family.

The peptides of the tachykinin family are widely distributed within the mammalian peripheral and central nervous systems and play a well-recognized role as excitatory neurotransmitters. Currently, the concept that tachykinins act exclusively as neuropeptides is being challenged, since the best known members of the family, substance P, neurokinin A and neurokinin B, are also present in non-neuronal cells and in non-innervated tissues. Moreover, the recently cloned mammalian tachykinins hemokinin-1 and endokinins are primarily expressed in non-neuronal cells, suggesting a widespread distribution and important role for these peptides as intercellular signaling molecules. The biological actions of tachykinins are mediated through three types of receptors denoted NK(1), NK(2) and NK(3) that belong to the family of G protein-coupled receptors. The identification of additional tachykinins has reopened the debate of whether more tachykinin receptors exist. In this review, we summarize the current knowledge of tachykinins and their receptors.

Development and potential utility of dual and triple NK receptor antagonists.

The mammalian tachykinin (TK) peptides and their three neurokinin (NK) receptors represent an effector system with wide-ranging actions on neuronal, airway smooth muscle, mucosal, endothelial, immune, inflammatory and remodeling cell function. Recent clinical and preclinical data suggests pathophysiological relevance for TKs in various diseases including asthma, emesis and depression. The promiscuous TK-NK receptor interactions and incompletely overlapping functions mediated by each NK receptor may indicate added therapeutic benefit of using multiple NK receptor blockade. Consequently, there has been substantial pharmaceutical effort in projects to develop nonpeptide dual and triple NK receptor antagonists. This review identifies the chemical and biological approach used to develop a TK antagonist active at the three NK receptors. Clinical activity has been observed using single and/or dual NK receptor antagonists in asthma, depression/anxiety and, most notably, emesis trials but no compound with mono or multiple NK receptor antagonist activities has cleared all the development and regulatory hurdles to commercialization. Current experience indicates that potent dual and triple NK receptor-selective antagonists possessing appropriate affinity and pharmacokinetic properties can be developed. As an example, the biological and pharmacokinetic profiles of a new representative of this class of agent, SCH 206272, is detailed in the present review. Whether such agents will fulfill researchers' expectations must await further clinical trials.

Structure-activity studies of bufokinin, substance P and their C-terminal fragments at bufokinin receptors in the small intestine of the cane toad, Bufo marinus.

Bufokinin is a substance P-related tachykinin peptide with potent spasmogenic actions, isolated from the intestine of the cane toad, Bufo marinus. Bufokinin acts via a tachykinin receptor with similarities to the mammalian NK(1) receptor. In this structure-activity study of bufokinin, substance P (SP) and their C-terminal fragments, we have used isolated segments and homogenates of toad small intestine to compare the contractile potencies and abilities to compete for the binding of [125I]-Bolton-Hunter bufokinin. In general, potency was very similar in both studies (r=0.956) and was primarily related to peptide length, with the natural undecapeptide tachykinins bufokinin - ranakinin>SP- cod SP -trout SP being most potent. The weakest peptides were [Pro(9)]SP, BUF(7-11) and SP(7-11). Bufokinin fragments (BUF) were approximately equipotent to the corresponding SP fragments, with only BUF(5-11) showing unexpectedly low binding affinity. Data obtained with SP, bufokinin and fragments were subjected to quantitative structure--activity (QSAR) analysis which demonstrated that molecular connectivity and shape descriptors yielded significant regression equations (r approximately 0.90). The predictive capacity of the equations was confirmed using ranakinin, trout SP and cod SP, but not using the synthetic analogs [Pro(9)]SP and [Sar(9)]SP. The study suggests that the full undecapeptide sequence of bufokinin is required for optimal activity, with high potency conferred by Lys(1), Pro(2), Gly(9) and probably Tyr(8). The finding that receptor-ligand interactions were correlated with the shape descriptor 2kappa(alpha) and favored by basic and rigid residues at position 1-3 is consistent with an important role of conformation at the N-terminus of bufokinin.

Actions of tachykinins within the heart and their relevance to cardiovascular disease.

Substance P and neurokinin A are tachykinins that are co-localized with calcitonin gene-related peptide (CGRP) in a unique subpopulation of cardiac afferent nerve fibers. These neurons are activated by nociceptive stimuli and exhibit both sensory and motor functions that are mediated by the tachykinins and/or CGRP. Sensory signals (e.g., cardiac pain) are transmitted by peptides released at central processes of these neurons, whereas motor functions are produced by the same peptides released from peripheral nerve processes. This review summarizes our current understanding of intracardiac actions of the tachykinins. The major targets for the tachykinins within the heart are the intrinsic cardiac ganglia and coronary arteries. Intrinsic cardiac ganglia contain cholinergic neurons that innervate the heart and coronary vasculature. Tachykinins can stimulate NK3 receptors on these neurons to increase their excitability and evoke spontaneous firing of action potentials. This action provides a mechanism whereby tachykinins can indirectly influence cardiac function and coronary tone. Tachykinins also have direct effects on coronary arteries to decrease or increase tone. Stimulation of NK1 receptors on the endothelium causes vasodilation mediated by nitric oxide. This effect is normally dominant, but NK2 receptor-mediated vasoconstriction can also occur and is augmented when NK1 receptors are blocked. It is proposed that these ganglion stimulant and vascular actions are manifest by endogenous tachykinins during myocardial ischemia.

Inflammatory and motor responses by tachykinins in the guinea-pig oesophageal sphincter.

1. The aim of this study was to characterize the tachykinin receptors involved in producing plasma protein extravasation and contractile responses of the guinea-pig oesophageal sphincter. 2. In anaesthetized guinea-pigs, the selective tachykinin NK-1 receptor agonist [Sar9,Met(O2)11]substance P produced plasma protein extravasation (PPE) which was not affected by the treatment with the tachykinin NK-2 receptor antagonist MEN 10627 (1 micromol kg(-1) i.v.) or the histamine H1-receptor antagonist, diphenhydramine (34.5 micromol kg(-1) i.v.). However, the [Sar9,Met(O2)11]substance P-induced PPE was blocked by the previous administration of the peptide tachykinin NK-1 receptor antagonist FK 888 or by the non-peptide antagonist SR 140333, yielding ED50 values of 1.1 +/- 0.2 and 0.01 +/- 0.004 micromol kg(-1) i.v., respectively. 3. The tachykinin NK-2 or NK-3 receptor agonists [beta-Ala8]neurokinin A (4-10) or [MePhe7]neurokinin B, respectively, produced a weak PPE at high doses. The effect of [MePhe7]neurokinin B-induced PPE was inhibited by SR 140333. 4. In the guinea-pig isolated oesophageal sphincter, [Sar9,Met(O2)11]substance P did not exert any contractile effect up to 10 microM. The selective tachykinin NK-2 receptor agonist ([beta-Ala8]neurokinin A (4-10), produced concentration-dependent contractions (pD2 = 7.6 +/- 0.03) which were inhibited by the selective tachykinin NK-2 receptor antagonist, MEN 10627 (pA2 = 8.6 +/- 0.1). Also, the tachykinin NK-3 receptor selective agonist [MePhe7]neurokinin B induced concentration-dependent contractile responses, but these responses were inhibited by MEN 10627. 5. Altogether, these data indicate that the stimulation of tachykinin NK-1 receptor produces a vascular inflammatory response, while activation of tachykinin NK-2 receptors mediate the contraction of the guinea-pig oesophageal sphincter.

Transglutaminase-synthesized gamma-(glutamyl5) spermidine derivative of substance P is a selective tool for neurokinin-2 receptors characterization.

The ability of transglutaminase-synthesized 1,3-diaminopropane, spermidine (Spd), spermine (Spm), and monodansylcadaverine gamma-(glutamyl5)derivatives of substance P (SP) to produce bronchoconstriction was investigated. In urethane-anaesthetized guinea pigs, intravenous injections of SP derivatives contracted differently bronchial smooth muscle and caused hypotension. The most effective bronchoconstrictor among SP analogs was the gamma-(glutamyl5)Spd derivative of SP (Spd-SP; EC50 = 5.3 nmol/kg), which was more potent than the native peptide (EC50 = 26.5 nmol/kg). In contrast, the gamma-(glutamyl5)Spm derivative of SP (Spm-SP) was found completely unable to cause bronchoconstriction and was significantly less effective than SP in determining hypotension. The contractile effect of Spd-SP and Spm-SP was investigated in vitro on rat isolated colon, a well-characterized preparation rich in NK2 receptors. In addition, Spd-SP was tested on the endothelium-denuded rabbit pulmonary artery (RPA) and the hamster isolated trachea (HT), both tissue preparations containing only a single functional receptor subtype (NK2A and NK2B, respectively). The results obtained showed that Spd-SP recognizes NK2 receptors occurring on rat isolated colon more effectively (EC50 = 11 nM) than the native peptide (EC50 = 45 nM). Conversely, Spm-SP evokes a contractile response less effective than that elicited by SP (EC50 = 312 nM). Furthermore, Spd-SP (0.1-10 microg kg(-1)) produced a concentration-dependent contraction of both HT and RPA, exhibiting a potency respectively 12 and 30 times higher than SP in contracting HT and RPA. Our results indicate that the introduction of a Spd moiety at the level of glutamine-5 of SP gives rise to an analog that possesses a different capability to recognize NK2 receptors than the parent peptide. Moreover, since Spd-SP seems to contract more effectively RPA than HT, we conclude that it preferentially recognizes the NK2A receptor subtype.

Tachykinin neuropeptide-evoked intracellular calcium transients in cultured guinea pig myenteric neurons.

Substance P and related tachykinins are present in the mammalian gut and act as neurotransmitters. Microfluorimetric measurement of intracellular calcium ([Ca2+]i) was used to study tachykinin-sensitive myenteric neurons. Substance P (0.001-10 microM) evoked concentration-dependent increases in percentage of neurons responding (6-75%) and delta [Ca2+]i (88 +/- 24 to 212 +/- 16 nM). Neurokinin A (0.001-1 microM) produced similar responses. Removal of extracellular Ca2+ abolished substance P-induced Ca2+ signals, as did the addition of the Ca2+ channel blockers lanthanum chloride (5 mM) and nickel chloride (2.5 mM). Both nifedipine (1-50 microM) and diltiazem (1-50 microM) inhibited substance P-evoked Ca2+ responses in a dose-dependent manner. Substance P and related tachykinins evoke Ca2+ signaling in cultured myenteric neurons by the influx of extracellular Ca2+ through L and N-type plasma membrane Ca2+ channels.

Further evidence that central tachykinin NK-1 receptors mediate the inhibitory effect of tachykinins on angiotensin-induced drinking in rats.

The order of potency of tachykinin (TK) receptor agonists suggests that TK NK-1 receptors mediate their inhibitory effect on water intake induced by intracerebroventricular (i.c.v.) injection of angiotensin II (AngII) in rats. The present study was aimed at further evaluating which TK receptor subtype mediates the effect, using selective antagonists for the TK receptor subtypes. Pulse i.c.v. injection of the TK agonist neuropeptide gamma (NP gamma), 31-250 ng/rat, markedly inhibited AngII-induced water intake. The i.c.v. injection of the NK-1 receptor antagonist SR14033, 0.5 microgram/rat, significantly reduced, while 1 microgram/rat completely abolished the inhibitory effect of NP gamma, 125 ng/rat. The selective NK-2 receptor antagonist SR48968 and the selective NK-3 receptor antagonist R820 were devoid of any effect up to the i.c.v. dose of 2 micrograms/rat. On the other hand, i.c.v. injection of SR140333, 1 microgram/rat, did not increase drinking induced by i.c.v. injection of AngII, 0.1-10 ng/rat, and did not increase drinking in water sated or water deprived rats. The results of the present study confirm that central TKergic mechanisms inhibit AngII-induced drinking in rats, and provide further evidence that TK NK-1 receptors mediate the effect. Failure of i.c.v. injected SR 140333 to increase AngII-induced drinking, as well as water intake in sated or deprived rats suggests that brain NK-1 receptor mechanisms apparently do not exert a tonic control on AngII-induced drinking and, in general, on water intake in rats. From a pharmacological point of view, the inhibitory effect of TKs on the dipsogenic action of AngII can represent a functional test for activity at central NK-1 receptors in rats.

Neurokinin-receptor antagonists: pharmacological tools and therapeutic drugs.

The mammalian tachykinins (substance P, neurokinin A, and neurokinin B) are widely distributed throughout the central and peripheral nervous systems, where they act as neurotransmitters or neuromodulators. Historically, the tachykinins have been implicated in a wide variety of biological actions such as pain transmission, neurogenic inflammation, smooth muscle contraction, vasodilation, secretion, and activation of the immune system. Their effects are mediated via specific G-protein-coupled receptors (NK1, NK2, and NK3 receptors). The development of nonpeptide receptor antagonists revealed species differences in neurokinin-receptor pharmacology, and the recent cloning of human neurokinin receptors has led to development of compounds with optimized affinity for the human target receptor. The neurokinin-receptor antagonists have been used in preclinical experiments to confirm the physiological roles of the tachykinins. Importantly, it is now recognised that these agents can inhibit the actions of tachykinins released from peripheral nerves, and for the NK1-receptor antagonists (the most widely studied class of neurokinin-receptor antagonists) central sites of action have also been demonstrated. These studies support the development of neurokinin-receptor antagonists as potentially exploitable drug therapies in humans, particularly in the treatment of pain and emesis.

Neurokinin receptors could be differentiated by their capacity to respond to the transglutaminase-synthesized gamma-(glutamyl5)spermine derivative of substance P.

Four different gamma-(glutamyl5)amine derivatives of substance P (SP) were synthesized in vitro in the presence of purified guinea pig liver transglutaminase and Ca2+. The 1,3-diaminopropane, spermidine, spermine (Spm), and monodansylcadaverine adducts of the neuropeptide were purified by HPLC on a reversed-phase column and characterized by fast atom bombardment mass spectrometry. The gamma-(glutamyl5)Spm derivative of SP (Spm-SP) was found to be able, like the parent neuropeptide, to provoke rabbit aorta relaxation, to decrease rat arterial blood pressure, and to inhibit collagen-induced platelet aggregation. Unlike SP, only a weak inflammatory response was observed when Spm-SP was injected in the rat hind limb. All these effects were found to be prevented by N omega-nitro-L-arginine methyl ester, a well-known nitric oxide synthesis inhibitor. In contrast, Spm-SP was completely ineffective in contracting guinea pig ileal segments, thus confirming our preliminary observations indicating that Spm-SP does not evoke SP-like spasmogenic effects on isolated smooth muscle preparations. The specificity of the effects due to the selective introduction of a Spm moiety at the glutamine5 level was demonstrated by the SP agonist pharmacological profile of the other gamma-(glutamyl5)amine derivatives tested. These results suggest that neurokinin receptors could be differentiated by their capacity to respond to Spm-SP.

Subtypes of tachykinin receptors on tonic and phasic neurones in coeliac ganglion of the guinea-pig.

1. Intracellular recording techniques were used to investigate the characteristics of tachykinin receptors and their subtypes in tonic and phasic neurones, which constituted two major neuronal populations in the coeliac ganglion of the guinea-pig. 2. In 95% of phasic neurones a long-lasting after-hyperpolarization (LAH), 5-8 s in duration and 10-20 mV in amplitude, was observed following action potentials evoked by passing a train of depolarizing current pulses into the neurones. In contrast, LAH was observed in only 4% of tonic neurones. 3. In most tonic neurones, substance P (SP), neurokinin A (NKA) and senktide induced depolarizations, whereas in phasic neurones they usually inhibited LAH but rarely induced depolarization. 4. Tonic and phasic neurones were further classified into three groups based on their responses (depolarization for tonic neurones and LAH inhibition for phasic neurones) to these tachykinin receptor agonists: (1) neurones responsive to SP, NKA and senktide (71-78%); (2) those responsive to senktide but not to SP and NKA (12-23%) and (3) those not responsive to any of the three agonists (7-11%). 5. GR71251 (5 microM), an NK1-selective tachykinin receptor antagonist, depressed the depolarization in tonic neurones and the LAH inhibition in phasic neurones induced by SP and NKA, but not those induced by senktide. 6. Selective NK2 receptor agonists, [Nle10]NKA4-10, [beta-Ala8]NKA4-10 and GR64349, were without effect in both tonic and phasic neurones. Furthermore, an NK2 receptor antagonist, L659,877, did not inhibit the depolarization induced by NKA, SP or senktide in tonic neurones. 7. It is suggested that NK1 and NK3 receptors are present on a large proportion of coeliac ganglion neurones. In tonic neurones both subtypes of tachykinin receptors are coupled to membrane depolarization,whereas in phasic neurones activation of these receptors leads to inhibition of LAH. The present study also suggests that NKA evokes the depolarization in tonic neurones and the LAH inhibition in phasic neurones via NK1, but not NK2 receptors.

Tachykinin receptors and receptor subtypes.

The tachykinins, substance P, neurokinin A and neurokinin B, are a family of neuropeptides widely distributed in the mammalian central and peripheral nervous system. In the peripheral nervous system, tachykinins released from peripheral endings of sensory nerves are responsible for the neurogenic inflammation phenomenon. In the spinal cord/central nervous system, tachykinins play a role in pain transmission/perception and in some autonomic reflexes and behaviors. Their actions are mediated by three distinct receptors, termed NK1, NK2 and NK3. All tachykinin receptors belong to the superfamily of G protein-coupled receptors, with seven putative transmembrane spanning segments. In the past few years, a number of potent and selective antagonists, of both peptide and nonpeptide nature, has been developed for the NK1, NK2 and NK3 receptors. The contemporary isolation and cloning of the three tachykinin receptors enable now to study the molecular determinants for the interaction of natural tachykinins with their receptors, and the mechanism by which the antagonists interfere in this process. Furthermore, the introduction of tachykinin antagonists has revealed a striking species-related heterogeneity among the tachykinin receptors, and has also suggested a possible intra-species heterogeneity for both NK1 and NK2 receptors. However, molecular biology studies are needed to prove the existence of true tachykinin receptor subtypes.

In vitro characterization of the non-peptide tachykinin NK1 and NK2-receptor antagonists, SR140333 and SR48968 in different rat and guinea-pig intestinal segments.

We investigated the potent non-peptide tachykinin receptor antagonists SR140333 and SR48968 for their ability to prevent the contraction of isolated intestinal tissues elicited by the non-selective agonists substance P (SP) and neurokinin A (NKA), or by [Sar9,Met(O2)11]SP and [beta-Ala8]NKA-(4-10) that are selective agonists for NK1 and NK2 receptors, respectively. In guinea-pig ileum, containing mainly NK1-receptors: SR140333 caused a pseudo-irreversible blockade of contractions induced by either SP (KB, 0.01 nM) or [Sar9,Met(O2)11]SP (KB, 0.03 nM); SR140333 but not SR48968, dose-dependently (IC50, 0.06 nM) antagonized the contractions elicited by capsaicin. In rat duodenum, containing mainly NK2 receptors, SR48968 caused a parallel rightward shift of the concentration-response curves of [beta-Ala8]NKA-(4-10) (pA2, 9.5), but not of NKA. In rat esophageal tunica muscularis mucosae, SR48968 non-competitively antagonized [beta-Ala8]NKA-(4-10) and NKA. SR48968 and SR140333 thus appear to be potent tachykinin receptor antagonists, selective for intestinal receptors respectively of the NK2 and NK1 type. The results also suggest that rat esophagus might contain a NK2-receptor subtype different from that of rat duodenum.

Neuroimmunomodulation: classical and non-classical cellular activation.

As neuroimmunologists, we are often faced with the fact that some substances can either enhance or inhibit particular immune/inflammatory cell functions. This 'duality' could only partially be explained by dose-dependency and the fact that in a variety of systems, heterogenous cell populations are commonly used. For example it has been repetitively shown that cell proliferation, immunoglobulin synthesis and NK (natural killer) activity could be enhanced, inhibited or not affected at all by such neuropeptides as somatostatin (SOM) or vasoactive intestinal peptide (VIP), depending on the experimental conditions. Even substance P (SP), which, in general, stimulates lymphocyte activity, can, under certain conditions, possess an inhibitory activity. These apparent discrepancies between various groups and experimental conditions met with a strong reservation among 'classical' immunologists as they questioned the true physiological role that neuro-immune interactions play in normal and disease states. However, upon a detailed analysis of the data, it become obvious why such discrepancies abounded. Not only are we comparing totally different responses in different species, but almost always we compare different experimental conditions. In lieu of this, the reproducibility of the experiments within the same laboratory is in fact very high. One fundamental and striking observation is the fact that at the level of a homogeneous cell population, a differential response could be evoked by the same neuropeptide over a range of concentrations. For the purpose of this brief report we will focus on the cellular responses to the neuropeptide substance P and we will try to illustrate why such differential responses are possible. Some of the physiological data relating to the effects of SP on cell function will be discussed. This will be followed by a synopsis of SP receptor mechanisms on effector cells and finally the mechanism by which SP activates secondary messenger systems in these cells.

Coexistence of three tachykinin receptors coupled to Ca++ signaling pathways in intestinal muscle cells.

Receptors for tachykinins and the signaling pathway to which they are coupled were characterized in dispersed muscle cells from the longitudinal muscle layer of the rat intestine. A technique of receptor protection whereby selective agonists and antagonists were used to protect one receptor while other receptors were inactivated with N-ethylmaleimide enabled each tachykinin receptor type to be identified separately. Protection of neurokinin (NK)-1 receptors with the selective NK-1 agonist, substance P methylester, or antagonist, GR-82,334 (Glp-Ala-Asp-Pro-Asn-Lys-Phe-Tyr-D-Pro[spiro-gamma-lactam]Leu-Trp-NH2), preserved the contractile response and increase in cytosolic-free Ca++ ([Ca++]i) induced by substance P methylester only; protection of NK-2 receptors with the selective NK-2 agonist, beta-[Ala8]NKA(4-10), or the selective NK-2b antagonist, L-659,877 [cyclo(Leu-Met-Gln-Trp-Phe-Gly)], preserved the contractile response and increase in [Ca++]i induced by beta-[Ala8]NKA(4-10) only; and protection of NK-3 receptors with the selective NK-3 agonist, senktide succinyl-[Asp6,MePhe8]substance P(6-11), preserved the contractile response and increase in [Ca++]i induced by succinyl-[Asp6,MePhe8]substance P(6-11) only. When used as a protective agent, the NK-2a antagonist, MEN-10,376 (H-Asp-Tyr-D-Trp-Val-D-Trp-D-Trp-Lys-NH2), did not preserve the response to any tachykinin agonist. Protection of NK-1, NK-2 and NK-3 receptors preserved fully the responses to the preferential endogenous agonists, substance P, NKA and NKB, respectively, but they also preserved in part (30-40%) the responses to the nonpreferential agonists. Because substance P and NKA are coreleased from the same precursor in intestinal muscle tissue, the pattern implied the existence of considerable spareness in the contractile response of muscle cells to tachykinins. Studies on dispersed circular muscle cells using selective tachykinin agonists as protective agents confirmed the presence of three tachykinin receptor types. The results demonstrate the coexistence of NK-1, NK-2b and NK-3 receptors on muscle cells of rat intestine that are preferentially activated by substance P, NKA and NKB, respectively, and are coupled separately to one signaling pathway mediating contraction.

Tachykinin NK1 receptor subtypes in the rat urinary bladder.

1. Following the recent proposal that the selective agonist septide, ([pGlu6,Pro9]SP(6-11)), acts on a novel tachykinin receptor distinct from the 'classical' NK1 receptor, the aim of the study was to investigate the possible heterogeneity of tachykinin NK1 receptors in the rat urinary bladder. 2. The synthetic tachykinin receptor agonists, septide (pD2 7.87) and [Sar9]substance P (SP) sulphone (pD2 7.64) produced concentration-dependent contractions of the rat isolated urinary bladder. 3. The NK1 receptor antagonists GR82,334, (+/-)-CP96,345, and RP67,580 competitively antagonized (slopes of Schild plot not significantly different from unity) the response to septide with the rank order of potency (pKB values in parentheses): RP 67,580 (7.57) > GR 82,334 (7.01) > (+/-)-CP 96,345 (6.80). The same antagonists were significantly less potent when tested against [Sar9]SP sulphone, while maintaining the same rank order of potency: RP 67,580 (7.00) > GR 82,334 (5.93) > (+/-)-CP 96,345 (< 6). The antagonists did not affect the concentration-response curve to bombesin. 4. To exclude the involvement of the NK2 receptor, a second series of experiments was performed in the presence of the potent nonpeptide NK2 receptor antagonist, SR 48,968. SR 48,968 (1 microM) produced a rightward shift of the concentration-response curve to the NK2 receptor selective agonist, [beta Ala8]neurokinin A (NKA) (4-10). SR 48,968 did not significantly modify the response to SP, NKA, neurokinin B (NKB), neuropeptide K (NPK), neuropeptide gamma (NP gamma), SP(4-11), SP(6-11), septide or [Sar9]SP sulphone. 5. In the absence or presence of SR 48,968, RP 67,580 antagonized in a competitive manner the response to septide, [Sar9]SP sulphone, SP(4-11) and SP(6-11): pKB values obtained in the absence and presence of SR 48,968 were not significantly different for any of these four agonists.6. RP 67,580 antagonized the response to SP and NKA both in the absence and presence of SR 48,968.In both cases, the slopes of the Schild plots were significantly different from unity. Mean dose-ratios produced by RP 67,580 in the presence of SR 48,968 were larger than those measured without NK2receptor blockade for both SP and NKA.7. RP 67,580 (3 MicroM) did not antagonize the response to NKB in the absence of SR 48,968. In the presence of SR 48,968, RP 67,580 acted as a competitive antagonist of NKB-induced contractions with apKB value (7.63) not significantly different from that measured towards septide. In the present of SR48,968, RP 67,580, GR 82,334 and (+/-)-CP 96,345 antagonized the response to NKB with a rank order of potency identical to that measured towards septide or [Sar9]SP sulphone.8. In the absence of SR 48,968, RP 67,580 (3 MicroM) produced a small shift of the concentration-response curve to neuropeptide K and was ineffective toward neuropeptide T. In the presence of SR 48,968 a clear shift of the curve to both agonists was observed.9. These findings are compatible with the idea that a septide-sensitive tachykinin receptor may exist in the rat urinary bladder. The septide-sensitive receptor is recognized by NK1 receptor antagonists with higher affinity than the 'classical' NK1 receptor recognized by [Sar9]SP sulphone. Our data suggest that NKB, after NK2 receptor blockade, is a more suitable ligand than SP for activation of the 'septidesensitive'receptor. While the final proof for the existence of possible NK1 receptor subtypes must await confirmation at the molecular level, the present findings provide strong pharmacological evidence that either NK, receptor subtypes or a novel type of tachykinin receptor exist in the rat urinary bladder.