Tachykinin receptor types: Classification and membrane signalling mechanisms

Involvement of neurokinin-1 receptors in the autonomic nervous system in colorectal distension-induced cardiovascular suppression in rats

Situational syncope, which includes rectally mediated reflexes, is defined as syncope induced by a specific situation. Its pathogenesis generally involves disorders of the autonomic nervous system. However, the mechanisms and preventive strategies are not yet well understood. Therefore, we hypothesized that a tachykinin neurokinin-1 receptor might be involved in the autonomic nervous system, and that a neurokinin-1 receptor antagonist could mitigate reflex syncope. This study used a rat model in which the reflex was induced by afferent vagal stimulation with colorectal distension (CRD). In the study, the rats were divided into three groups: non-CRD, CRD, and CRD with a neurokinin-1 receptor antagonist. First, we examined the effect of fosaprepitant, a neurokinin-1 receptor antagonist, on the circulatory response in this model. We then determined the brain regions that showed increased numbers of c-Fos immunoreactive cells in the respective groups. Our results suggest that the colorectal distension procedure reduced blood pressure and that fosaprepitant lowered this response. In addition, the number of c-Fos immunoreactive cells was increased in the caudal ventrolateral medullary region with colorectal distension, and this number was decreased by the administration of fosaprepitant. In conclusion, fosaprepitant might be involved in the vagal reflex pathway and potentially suppress the circulatory response to colorectal distension.

Crosstalk between neurokinin receptor signaling and neuroinflammation in neurological disorders

The neurokinin 1 receptor with the natural substrate substance P is one of the intensely studied receptors among the neurokinin receptors. The intracellular signaling mechanism uses G protein-coupled transduction regulating various physiological processes from nausea to Alzheimer's disease. The neurokinin 1 receptor plays a significant role in neuroinflammation-mediated alterations in neural circuitry. Neurokinin 1 receptor antagonists are selective, potent and exhibited efficacy in animal models of nervous system disorders. Evolving data now strengthen the viewpoint of brain substance P/neurokinin 1 receptor axis-mediated action in neural circuit dysfunction. Thus, a deep-rooted analysis of disease mechanism in which the neurokinin 1 receptor is involved is necessary for augmenting disease models which encourage the pharmaceutical industry to intensify the research pipeline. This review is an attempt to outline the concept of neurokinin 1 receptor signaling interlinked to the brain innate immune system. We also uncover the mechanisms of the neurokinin 1 receptor involved in neurological disorder and various methods of modulating the neurokinin 1 receptor, which may result in therapeutic action.

Biochemical and Pharmacological Characterization of a Mice Model of Complex Regional Pain Syndrome

BACKGROUND AND OBJECTIVES

Complex regional pain syndrome is a challenging disease to treat. Recently, a mouse fracture model of complex regional pain syndrome has been developed that has many signs of the clinical syndrome. However, many aspects of the sensory neuron biochemistry and behavioral and pharmacological characterization of this model remain to be clarified.

METHODS

Mice were randomly assigned to fracture/cast or control (naive) groups. Fracture/cast mice underwent a closed distal tibia facture, with hindlimb wrapped in casting tape for 3 weeks. After cast removal, mice were tested for mechanical allodynia, burrowing behavior, and motor ability over a 12-week period. Protein immunohistochemistry was performed for substance P, calcitonin gene-related peptide, tropomyosin receptor kinase A, nerve growth factor, Nav1.7, and transient receptor potential cation-channel V1, colocalized in neurons, in the ipsilateral lumbar dorsal root ganglia (DRGs). Analgesic drugs were tested for pain-relieving efficacy.

RESULTS

Mechanical allodynia was greater in the ipsilateral hindpaw (P = 0.0002) in the fracture/cast group versus the control group, over the 3- to 12-week period. The amount of burrowing material removed was decreased (P = 0.0026), and there were deficits in spontaneous motor-rearing behavior (P = 0.018). Immunostaining of substance P, calcitonin gene-related peptide, Trk A receptor, nerve growth factor, Nav1.7, and transient receptor potential cation-channel V1 all demonstrated up-regulation in the DRGs of fracture mice versus controls (all P < 0.05). Morphine, pregabalin, ketamine, acetaminophen, and dexamethasone transiently increased force withdrawal thresholds on the ipsilateral (fracture) side and improved burrowing activity after injection (all P < 0.05). Ketorolac improved only burrowing.

CONCLUSIONS

Persistent pain-related behavior was demonstrated in this mouse fracture/cast model with wide-scale DRG up-regulation of pain mediators. Antihyperalgesic drugs reduced mechanical allodynia and improved burrowing.

Substance P and the neurokinin-1 receptor expression in dog ileum with and without inflammation

In the gastrointestinal tract, the tachykinin Substance P (SP) is involved in motility, fluid and electrolyte secretion, and blood flow and regulation of immunoinflammatory response. SP exerts its biological activity on target cells by interacting mainly with the neurokinin-1 receptor (NK₁R). The present study aims to quantify the percentage of SP-immunoreactive (SP-IR) enteric neurons and the density of SP-IR nerve fibers in the ileum of control dogs (CTRL-dogs; n=7) vs dogs with spontaneous ileal inflammation (INF-dogs; n=8). In addition, the percentage of enteric neurons bearing NK₁R, and nitrergic neurons (nNOS-IR) expressing NK₁R immunoreactivity were evaluated in both groups. The percentages of SP-IR neurons were similar in CTRL- and INF-dogs, in either the myenteric (MP) (15±8% vs. 16±7%, respectively) and submucosal plexus (SMP) (26±7% vs. 24±14%, respectively). In INF-dogs, the density of SP-IR mucosal nerve fibers showed a trend to decrease (P=0.07). Myenteric neurons of CTRL- and INF-dogs expressed similar percentages of NK₁R-immunoreactivity (39±5% vs. 38±20%, respectively). Submucosal NK₁R-IR neurons were occasionally observed in a CTRL-dog. MP nitrergic neurons bearing NK₁R showed a trend to decrease in INF-dogs vs. CTRL- dogs (41±22% vs. 65±10%, respectively; P=0.11). In INF-dogs, muscle cells and immune cells overexpressed NK₁R immunoreactivity. These findings should be taken as a warning for possible intestinal motility disorders, which might occur during administration of NK₁R-antagonist drugs. Conversely, the strong expression of NK₁R immunoreactivity observed in muscle and mucosal immune cells of inflamed tissues may provide a rationale for the use of NK₁R antagonist drugs in the treatment of intestinal inflammation.

Substance P Regulation in Epilepsy

Background:

Epilepsy is a common neurological disease characterized by abnormal temporary discharge of neurons in the central nervous system. In recent years, studies have revealed the localization and changes in the density of neuropeptides, such as substance P (SP) in the pathogenesis of epilepsy. This review is a concise overview of SP and their physiologic and pathologic functions on regulating epilepsy, and the underline mechanisms.

Methods:

We research and collect relative online content for reviewing the effects of SP in Epilepsy.

Results:

The SP/NK-1 receptor system may induce seizures and play an important role in status epilepticus and in experimental animal models of epilepsy. Newest studies show that several mechanisms may explain the excitatory effects of the SP/NK-1 receptor signaling pathway in epilepsy. By binding to the NK-1 receptor, NK-1 receptor antagonists may block the pathophysiological effects of SP, and further studies are needed to confirm the possible anti-epileptic activity of NK-1 receptor antagonists.

Conclusion:

SP plays crucial roles on through binding with NK-1 receptor during epilepsy pathologic processing, and the NK-1 receptor is receiving a great attention as a therapeutic target for treating epilepsy. Thus, the use of NK-1 receptor antagonists for the treatment of epilepsy should be investigated in further studies.

Role of substance P in the cardiovascular system

This article provides an overview of the structure and function of substance P signalling system and its involvement in the cardiovascular regulation. Substance P is an undecapeptide originating from TAC1 gen and belonging to the tachykinin family. The biological actions of substance P are mainly mediated through neurokinin receptor 1 since substance P is the ligand with the highest affinity to neurokinin receptor 1. Substance P is widely distributed within the central and peripheral nervous systems as well as in the cardiovascular system. Substance P is involved in the regulation of heart frequency, blood pressure and in the stretching of vessels. Substance P plays an important role in ischemia and reperfusion and cardiovascular response to stress. Additionally, it has been also implicated in angiogenesis, pain transmission and inflammation. The substance P/neurokinin receptor 1 receptor system is involved in the molecular bases of many human pathological processes. Antagonists of neurokinin receptor 1 receptor could provide clinical solutions for a variety of diseases. Neurokinin receptor 1 antagonists are already used in the prevention of chemotherapy induced nausea and vomiting.

Biological and Pharmacological Aspects of the NK1-Receptor

The neurokinin 1 receptor (NK-1R) is the main receptor for the tachykinin family of peptides. Substance P (SP) is the major mammalian ligand and the one with the highest affinity. SP is associated with multiple processes: hematopoiesis, wound healing, microvasculature permeability, neurogenic inflammation, leukocyte trafficking, and cell survival. It is also considered a mitogen, and it has been associated with tumorigenesis and metastasis. Tachykinins and their receptors are widely expressed in various human systems such as the nervous, cardiovascular, genitourinary, and immune system. Particularly, NK-1R is found in the nervous system and in peripheral tissues and are involved in cellular responses such as pain transmission, endocrine and paracrine secretion, vasodilation, and modulation of cell proliferation. It also acts as a neuromodulator contributing to brain homeostasis and to sensory neuronal transmission associated with depression, stress, anxiety, and emesis. NK-1R and SP are present in brain regions involved in the vomiting reflex (the nucleus tractus solitarius and the area postrema). This anatomical localization has led to the successful clinical development of antagonists against NK-1R in the treatment of chemotherapy-induced nausea and vomiting (CINV). The first of these antagonists, aprepitant (oral administration) and fosaprepitant (intravenous administration), are prescribed for high and moderate emesis.

[Mechanism of spinal pain transmission and its regulation]

Morphine has been widely used for the treatment of acute, chronic, and cancer pain and is considered the strongest analgesic in clinical care. Conversely, morphine-induced analgesia may be accompanied by several side effects. Animal studies have demonstrated that low doses of morphine administered intrathecally can produce reliable analgesia for thermal, mechanical, and chemical nociceptive stimulation. On the other hand, high doses of morphine administered intrathecally may induce spontaneous nociceptive responses such as scratching, biting, and licking in mice as well as agitation and vocalization in rats. In addition, similar nociceptive responses including hyperalgesia, allodynia, and myoclonus have been observed in humans following intrathecal or systemic administration of high-dose morphine. It has been suggested that the spontaneous nociceptive behaviors evoked by high-dose morphine may be mediated by a non-opioid mechanism that is not yet fully understood. This review describes the mechanisms of spontaneous nociceptive behaviors evoked by high-dose morphine focusing on the neurotransmitters/neuromodulators released from primary afferent fibers.

Roles of substance P and ATP in the subepithelial fibroblasts of rat intestinal villi

The ingestion of food and water induces chemical and mechanical signals that trigger peristaltic reflexes and also villous movement in the gut. In the intestinal villi, subepithelial fibroblasts under the epithelium form contractile cellular networks and closely contact to the varicosities of substance P and nonsubstance P afferent neurons. Subepithelial fibroblasts of the duodenal villi possess purinergic receptor P2Y1 and tachykinin receptor NK1. ATP and substance P induce increase in intracellular Ca(2+) and cell contraction in subepithelial fibroblasts. They are highly mechanosensitive and release ATP by mechanical stimuli. Released ATP spreads to form an ATP "cloud" with nearly 1μM concentration and activates the surroundings via P2Y1 and afferent neurons via P2X receptors. These findings suggest that villous subepithelial fibroblasts and afferent neurons interact via ATP and substance P. This mutual interaction may play important roles in the signal transduction of mechano reflex pathways including a coordinate villous movement and also in the maturation of the structure and function of the intestinal villi.

Enhanced nerve-stimulated muscarinic and neurokinin contractions of ileum from streptozotocin guinea-pigs

Diabetes mellitus can lead to neuropathy of enteric neurons, resulting in abnormal gut motility. These studies investigated voltage-dependent contributions of muscarinic M₃ receptor activation by acetylcholine and neurokinin NK₁ receptor activation by neurokinins to nerve-stimulated contractions of longitudinal ileal strips from STZ guinea-pigs, a type 1 diabetic model with insulin deficiency, but mild hyperglycaemia. Contractions to bethanechol, substance P methyl ester, and nerve stimulation were greater in diabetic as compared to control ileum. The muscarinic M₃ receptor antagonist 4-DAMP at lower voltages and the neurokinin NK₁ receptor antagonist SR140333 at higher voltages, but not the neurokinin NK₁ receptor antagonist CP-96,345, were more effective at inhibiting nerve-stimulated immediate peak contractions and total areas of contraction of ileum from diabetic as compared to control animals. For diabetic ileum, voltage-dependent increases in the areas of nerve-stimulated contraction were observed in the presence of 4-DAMP and CP-96,345 but not SR140333. At low voltages only, nerve-stimulated release of acetylcholine was greater from diabetic as compared to control ileum. Fluorescence intensity of tachykinin-like immunoreactivity was increased in ileal myenteric ganglia from diabetic as compared to control animals. In diabetic guinea-pigs, stronger ileal nerve-stimulated contractions reflected increased release of acetylcholine at lower voltages and tachykinins at higher voltages, as well as increased sensitivity of smooth muscle M₃ and NK₁ receptors to acetylcholine and tachykinins. Hypoinsulinaemia may be a primary contributor to intestinal motility dysfunction in type 1 diabetes mellitus.

Testicular toxicity induced by a triple neurokinin receptor antagonist in male dogs

Mechanism mediating the testicular toxicity induced by CS-003, a triple neurokinin receptor antagonist, was investigated in male dogs. Daily CS-003 administrations showed testicular toxicity, such as a decrease in the sperm number, motility and prostate weight; and an increase in sperm abnormality, accompanying histopathological changes in the testis, epididymis and prostate. A single CS-003 administration suppressed plasma testosterone and LH levels in intact and castrated males. The suppressed LH release was restored by GnRH agonist injection, suggesting that pituitary sensitivity to GnRH is not impaired by CS-003. Treatment with SB223412, a neurokinin 3 receptor antagonist, caused a similar effect to CS-003, such as toxicity in the testis, prostate and epididymis and decreased plasma level of LH and testosterone. In conclusion, CS-003-induced testicular toxicity is caused by the inhibition of neurokinin B/neurokinin 3 receptor signaling probably at the hypothalamic level in male dogs.

Three days after a single exposure to ozone, the mechanism of airway hyperreactivity is dependent on substance P and nerve growth factor

Ozone causes persistent airway hyperreactivity in humans and animals. One day after ozone exposure, airway hyperreactivity is mediated by release of eosinophil major basic protein that inhibits neuronal M(2) muscarinic receptors, resulting in increased acetylcholine release and increased smooth muscle contraction in guinea pigs. Three days after ozone, IL-1β, not eosinophils, mediates ozone-induced airway hyperreactivity, but the mechanism at this time point is largely unknown. IL-1β increases NGF and the tachykinin substance P, both of which are involved in neural plasticity. These experiments were designed to test whether there is a role for NGF and tachykinins in sustained airway hyperreactivity following a single ozone exposure. Guinea pigs were exposed to filtered air or ozone (2 parts per million, 4 h). In anesthetized and vagotomized animals, ozone potentiated vagally mediated airway hyperreactivity 24 h later, an effect that was sustained over 3 days. Pretreatment with antibody to NGF completely prevented ozone-induced airway hyperreactivity 3 days, but not 1 day, after ozone and significantly reduced the number of substance P-positive airway nerve bundles. Three days after ozone, NK(1) and NK(2) receptor antagonists also blocked this sustained hyperreactivity. Although the effect of inhibiting NK(2) receptors was independent of ozone, the NK(1) receptor antagonist selectively blocked vagal hyperreactivity 3 days after ozone. These data confirm mechanisms of ozone-induced airway hyperreactivity change over time and demonstrate 3 days after ozone that there is an NGF-mediated role for substance P, or another NK(1) receptor agonist, that enhances acetylcholine release and was not present 1 day after ozone.

Effects of ischemia on tachykinin-containing nerves and neurokinin receptors in the rabbit bladder

OBJECTIVES

Our previous studies showed marked changes in efferent nerve structure and reactivity in the ischemic bladder. The goal of this study was to examine the effects of bladder ischemia on tachykinin (TK) containing sensory nerves and neurokinin receptors (NKR) in a rabbit model.

METHODS

We recorded bladder blood flow and spontaneous contractions in treated animals at week 8 after the induction of iliac arteries atherosclerosis and in age-matched controls. Bladder tissues were processed for studies of isometric smooth muscle tension in the organ bath, NK2R gene expression using quantitative real-time polymerase chain reaction (PCR), immunohistochemical staining of TK containing nerves and epithelial TK expression, and transmission electron microscopy.

RESULTS

Atherosclerosis-induced ischemia significantly increased the frequency of spontaneous bladder contractions in vivo. Electrical field stimulation (EFS)-induced smooth muscle contractions were significantly greater in the ischemic tissues. Inhibition of NK1R diminished contractions to low-frequency EFS in control tissues while having no significant effect on the ischemic tissues. In contrast, NK2R inhibition significantly decreased contractions to both low- and high-frequency EFS in the ischemic tissues. Inhibition of NK3R had no significant effect on EFS-induced contractions. Real-time PCR showed a significant increase in NK2R gene expression in the ischemic bladder. The number of TK immunopositive nerves and epithelial TK immunoreactivity were significantly greater in the ischemic bladder. These alterations were associated with marked ultrastructural reactions to bladder ischemia.

CONCLUSIONS

Alterations of NK2R reactivity and gene expression, increased number of TK immunopositive nerves, and greater epithelial TK immunoreactivity may imply activated bladder afferents to signal ischemic insult.

Process development and large-scale synthesis of NK1 antagonist

A scaleable synthetic route is described to obtain 2-(4-acetylpiperadin-1-yl)-6-[3,5-bis(trifluoromethyl)phenylmethyl]-4-(2-methylphenyl)-6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one (1, KRP-103) as a neurokinin (NK)(1) antagonist. The key step in the synthesis is the intramolecular cyclization of N-[3,5-bis(trifluoromethyl)phenylmethyl]-N-(3-hydroxypropyl)-4-chloro-6-(2-methylphenyl)-2-methylthiopyrimidine-5-carboxamide (15) which was obtained by amide formation between 4-(2-methylphenyl)-2-methylthio-6-oxo-1,6-dihydropyrimidine-5-carboxylic acid (8) and 3-[3,5-bis(trifluoromethyl)phenylmethylamino]-1-propanol (3). Treatment of 15 with 1,8-diazabicyclo[5,4,0]undec-7-ene provided 6-[3,5-bis(trifluoromethyl)phenylmethyl]-4-(2-methylphenyl)-2-methylthio-6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one (6). This intermediate (6) is transformed into the candidate compound (1) by two steps; oxidation, and substitution reaction of the resultant sulfone (7) with 1-acetylpiperazine. This synthetic method is free of chromatographic purification and is amenable to large scale synthesis.

Analysis of crucial structural requirements of 2-substituted pyrimido[4,5-b][1,5]oxazocines as NK1 receptor antagonist by axially chiral derivatives

This study aimed to identify the crucial structural features of 2-substituted 8-methylpyrimido[4,5-b][1,5]oxazocine derivatives. Axially chiral 8-methylpyrimido[4,5-b][1,5]oxazocines bearing a substituent at the C-2 position were synthesized and evaluated as NK(1) antagonists. The results revealed that (aR, 8S)-stereochemistry and the substituent at the C-2 position are important for NK(1) receptor recognition.

Mechanisms of relaxing response induced by rat/mouse hemokinin-1 in porcine coronary arteries: roles of potassium ion and nitric oxide

Rat and mouse hemokinin-1(r/m hemokinin-1) is a recently described member of the tachykinin family whose cardiovascular functions are not fully understood. In this study, we investigated the mechanisms of the relaxing response induced by r/m hemokinin-1 in isolated porcine coronary arteries by using a specific antagonist of tachykinin NK(1) receptor (SR140333), a nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NNA), and 1H-[1,2,4] Oxadiazolo [4,3-a] quinoxalin-1-one (ODQ), a blocker of cGMP production. r/m Hemokinin-1 (10(-12)-10(-6 )M) evoked a marked endothelium-dependent vasodilatation (E(max)=121.12+/-10.6% and 91.79+/-2.39% in 10(-6) M PGF(2)alpha and 30 mM KCl precontracted arterial rings, respectively) of coronary arteries mediated by activation of endothelial tachykinin NK(1) receptors. Two components contributed to this r/m hemokinin-1-elicited vasodilatation, the first of which was endothelium-derived hyperpolarizing factor (EDHF), which played a major role. This EDHF was identified as a potassium current through certain kinds of potassium channels on the endothelial cell membrane of porcine coronary arteries. Specific antagonists of Ca(2+)-activated K(+) channels (dequalinium and clotrimazole) did not have an inhibitory effect on the r/m hemokinin-1-induced vasodilatation, whereas they did on the substance P-induced vasodilatation. When potassium ion efflux was impaired by a high K(+) concentration (30 mM) or removal of K(+) from the surroundings, NO synthesis was triggered by r/m hemokinin-1 to produce an equivalent EDHF (K(+))-independent vasorelaxation as a compensatory mechanism.

Tachykinins and excitotoxicity in cerebellar granule cells

The tachykinins represent an important group of neuropeptides that are widely distributed both in the central and peripheral nervous system where they perform several functions connected with neuronal modulation, often in synergy with glutamate excitatory transmission. While a great deal of data is available on their distribution and many studies have been performed by molecular, biochemical, and immunohistochemical techniques, much less is known about their physiological role, in particular in the cerebellum. This review is an attempt to summarize the diverse evidence suggesting a role for tachykinins in cerebellar granule neurons.

Cyclic urea derivatives as potent NK1 selective antagonists

A series of novel five- and six-membered ring urea derivatives have been described as potent and selective NK1 receptor antagonists. Several compounds in this series exhibited good oral activity and brain penetration. Syntheses of these compounds are also described herein.

Design, synthesis, and evaluation of novel 2-substituted-4-aryl-6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-ones as NK1 antagonists

A series of novel bicyclic pyrimidine derivatives was prepared as part of a search for NK1 antagonist aimed at the treatment of urinary incontinence. Among them, 3g, a pyrimido[4,5-b][1,5]oxazocine derivative, bearing a 4-acetylpiperazinyl group and a 2-methylphenyl group, was shown to have potent NK1 antagonist activity with a K(B) value of 0.105 nM and markedly increased the effective bladder capacity of guinea pigs (59.4% at 0.3 mg/kg iv and 62.8% at 3 mg/kg id). Furthermore, the effect of 3g on bladder function appeared to differ from that of tolterodine, another classical anti-pollakiuria agent, as determined by the distention-induced rhythmic bladder contraction assay using a urethane-anesthetized guinea pig model. Compound 3g is expected to be a promising agent for the treatment of urinary incontinence.

Effects of substance P on mesenteric lymphatic contractility in the rat

BACKGROUND

Substance P (SP) is associated with lymphatic tissue and is a putative mediator of inflammation. The lymph pump is one of the major "safety factors" preventing edema and its activity is altered by inflammatory mediators. The impact of SP on lymphatics was studied in the rat mesentery.

METHODS AND RESULTS

Rats were prepared for in situ lymphatic observation using intravital videomicroscopic techniques. Sections of the small intestine and mesentery were exteriorized and superfused. Lymphatic diameters were measured and pumping activity was determined from the lymphatic diameter tracing. Lymph pump parameters evaluated included diastolic diameter, systolic diameter, contraction frequency, stroke volume, and lymph pump flow. After a control period, the tissues were exposed to SP (10(-9), 10(-8), 10(-7), 10(-6) M). SP reduced both diameters and increased contraction frequency in a concentration-dependent manner. SP (1.0 microM) produced the following changes (% of control): reductions in diastolic diameter (50%), systolic diameter (55%), and stroke volume (63%); a large increase in contraction frequency (661%); and a modest increase in lymph pump flow (44%). SP also stimulated vessels that were not contracting phasically to develop typical contraction patterns.

CONCLUSIONS

Although SP produced a tonic constriction of the lymphatics, lymph pump flow was maintained or slightly elevated via an increase in contraction frequency. SP also induced pumping activity in lymphatics that were previously quiescent, thereby further stimulating flow. These effects may serve to minimize the formation of edema in face of the inflammatory edemagenic conditions produced by SP.

Design and synthesis of novel 9-substituted-7-aryl-3,4,5,6-tetrahydro-2H-pyrido[4,3-b]- and [2,3-b]-1,5-oxazocin-6-ones as NK1 antagonists

Novel 9-substituted-7-aryl-3,4,5,6-tetrahydro-2H-pyrido[4,3-b]- and [2,3-b]-1,5-oxazocin-6-ones were designed and prepared as part of a search for NK1 antagonists. Structure-activity relationship studies indicated that the conformational restriction resulting from the incorporation of an oxazocine ring and the presence of a terminal heteroatom on the cyclic amino group at the C-9 position play important roles in NK1, receptor recognition.

Synthesis of a Potent hNK-1 Receptor Antagonist via an SN2 Reaction of an Enantiomerically Pure α-Alkoxy Sulfonate

The concise synthesis of a stereochemically rich hNK-1 receptor antagonist is described. The synthesis is highlighted by an S(N)2 reaction of an enantiomerically pure alpha-alkoxy sulfonate (orthogonally protected butane triol), which was prepared by utilizing salen-mediated hydrolytic kinetic resolution technology. A stereocontrolled acetalization was employed to connect two enantiomerically pure fragments with a high degree of diastereoselectivity.

Expression of neurokinin a receptor mRNA in human nasal mucosa

In airway tissues, it has been suggested that tachykinins act as the transmitter for afferent sensory nerves which respond to various irritants and may be involved in airway allergic reactions. Three classes of tachykinin receptor have been recognized, denoted NK1, NK2 and NK3, which exhibit preferential affinity for substance P, neurokinin A and neurokinin B, respectively. We used molecular probes to study the gene expression and distribution of NK2 receptor in human nasal mucosa. Total RNA was isolated from human nasal mucosa and NK2 receptor mRNA was detected in these tissues using reverse transcriptase polymerase chain reaction (RT-PCR). For an in situ hybridization study of human nasal mucosa, we utilized the PCR directly to incorporate a T7 RNA polymerase promoter sequence onto the NK2 receptor cDNA, and these PCR products were used as the DNA template for producing digoxigenin-labeled antisense and sense RNA probes. These studies revealed that NK2 receptor mRNA was expressed in blood vessels. The results suggest a primary role for neurokinin A in the form of vascular responses in the upper respiratory tract.

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.

Localization of neurokinin 1 receptor (NK1R) immunoreactivity in rat esophagus

The aim of the present immunohistochemical study was to investigate the localization of neurokinin 1 receptor (NK1R) in rat esophagus and examine the relationship between NK1Rs and intrinsic cholinergic, nitrergic, or substance P (SP) neurons. NK1R immunoreactivity (IR) was observed on the nerve cell bodies in the myenteric ganglia throughout the esophagus, but not on striated muscles and smooth muscle cells of the muscularis mucosae. The frequency of occurrence of NK1R neurons was highest in the cervical esophagus and lowest in the lower thoracic esophagus. Considerable immunoreactivity was seen on the nerve cell surfaces and was also present in the cytoplasm of cell somas and in the initial part of the axons, but not in any other nerve fibers or terminals. Dogiel type I-like morphology was observed in some of the NK1R neurons; however, the majority exhibited polymorphic morphology. Double immunolabeling indicated that a majority (77%) of the NK1R neurons were immunoreactive for choline acetyltransferase (ChAT), while a minority (23%) were immunoreactive for nitric oxide synthase (NOS)-IR. Most of the NK1R neurons (92%) were innervated by the SP nerve fibers. Triple immunolabeling indicated that 70% of the NK1R neurons were associated with intrinsic SP nerve fibers (without CGRP-IR), 59% were associated with extrinsic SP nerve fibers (with CGRP-IR), and 35% were associated with both intrinsic and extrinsic SP nerve fibers. These results suggest that SP/tachykinin released from the SP nerve fibers of intrinsic and/or extrinsic origin activates the predominantly intrinsic cholinergic neurons via NK1Rs to influence neuronal transmission or motility in rat esophagus.

Autoradiographic distribution of tachykinin NK2 binding sites in the rat brain: comparison with NK1 and NK3 binding sites

The autoradiographic distribution of tachykinin NK(2) binding sites was determined in the adult rat brain using [(125)I]neurokinin A in the presence of either senktide (NK(3) agonist) and [Pro(9)]substance P (NK(1) agonist) or senktide and SR 140333 (NK(1) antagonist). Indeed, this radioligand labels two subtypes of NK(1) binding sites (which present a high affinity not only for SP but also for neurokinin A, neuropeptide K and neuropeptide gamma) as well as NK(3) binding sites. The distribution of NK(2) binding sites was also compared with those of NK(1) and NK(3) binding sites, these sites being labeled with [(125)I]Bolton and Hunter substance P and [(125)I]Bolton and Hunter eledoisin, respectively. In agreement with our results obtained with membranes from various brain structures, NK(2)-sensitive [(125)I]neurokinin A labeling was mainly observed in few structures including the dorsal and ventral hippocampus, the septum, the thalamus and the prefrontal cortex. The density of NK(2) binding sites was weak when compared with those of NK(1) and NK(3) binding sites. Marked differences were observed in the distributions of NK(1), NK(2) and NK(3) binding sites. These results are discussed taking into consideration differences or similarities between the distributions of NK(2)-sensitive [(125)I]neurokinin A binding sites and of their endogenous ligands (neurokinin A, neuropeptide K and neuropeptide gamma) but also local NK(2) agonist responses blocked by NK(2) antagonists. Insights on the roles of endogenous tachykinins in several brain functions are also discussed on the basis of the respective distributions of different neurokinin binding sites.

Tachykinin NK3 and NK1 receptor activation elicits secretion from porcine airway submucosal glands

1 We presently characterized the tachykinin receptor subtypes, using tachykinin receptor agonists and selective antagonists, that induce submucosal gland fluid flux (J(G)) from porcine tracheal explants with the hillocks technique. We also investigated the effects of the tachykinin receptor agonists on the electrophysiologic parameters of the tracheal epithelium in Ussing chambers. 2 The NK(1) tachykinin receptor agonist substance P (SP, 1 microM) and the NK(3) tachykinin receptor agonist [MePhe(7)]neurokinin B ([MePhe(7)]NKB, 1 microM) induced gland fluid fluxes of 0.29+/-0.03 microl min(-1) cm(-2) (n=26) and 0.36+/-0.05 microl min(-1) cm(-2) (n=24), respectively; while the NK(2) tachykinin receptor agonist [betaAla(8)]neurokinin A (4-10) ([betaAla(8)]NKA (4-10), 1 microM) had no effect on J(G) (n=10). 3 The NK(1) receptor antagonist CP99994 (1 microM, n=9) blocked 93% of the SP-induced J(G), whereas the NK(3) receptor antagonist SB223412 (1 microM, n=12) had no effect on the SP-induced J(G). However, SB223412 (1 microM, n=9) blocked 89% of the [MePhe(7)]NKB-induced J(G) while CP99994 (1 microM, n=10) did not affect the [MePhe(7)]NKB-induced J(G). The NK(2) receptor antagonist SR48968 (1 microM) did not block the J(G) induced by either the NK(1) (n=4) or NK(3) (n=13) receptor agonists. 4 The nicotinic ganglionic acetylcholine receptor antagonist hexamethonium (1 microM) and the muscarinic acetylcholine receptor antagonist atropine (1 microM) also decreased the NK(3) receptor agonist-induced J(G) by 67% (n=10) and 71% (n=12), respectively. 5 The potential difference (PD), short-circuit current (I(SC)), and membrane resistance (R(M)) of the porcine tracheal epithelial membranes were not significantly affected by any of the neurokinin agonists or antagonists (1 microM, basolateral) used in this study, although SP and [betaAla(8)]NKA (4-10) induced a slight transient epithelial hyperpolarization. 6 These data suggest that NK(1) and NK(3) receptors induce porcine airway gland secretion by different mechanisms and that the NK(3) receptor agonists induced secretion is likely due to activation of prejunctional NK(3) receptors on parasympathetic nerves, resulting in acetylcholine-release. We conclude that tachykinin receptor antagonists may have therapeutic potential in diseases with pathophysiological mucus hypersecretion such as asthma and chronic bronchitis.

Circular versus longitudinal myometrial contractile response to selective tachykinin receptor agonists in rat

This study compared the nature and magnitude of the contractile response produced in vitro by selective NK1, NK2 and NK3 tachykinin receptor agonists in circularly and longitudinally oriented strips of myometrium from ovariectomised and ovariectomised oestrogen-treated rats. The nature of the responses produced upon stimulation of the tachykinin receptors varied between the different myometrial preparations and the hormonal environment from which the tissue was taken. Variations included: (i) sustained contraction until washout of agonist; (ii) biphasic contraction until washout of agonist; and (iii) monophasic contraction. The major differences in magnitude of contractions were seen in preparations from oestrogen-treated animals in which responses to stimulation of all tachykinin receptors were reduced in comparison to preparations from non-oestrogen treated animals. Furthermore, the responses in circularly oriented myometrium preparations from oestrogen-treated animals were all markedly reduced compared to responses in longitudinally oriented myometrium preparations. These results suggest that the tachykinin receptors in longitudinally and circularly oriented myometrial layers are differentially regulated, especially in tissue isolated from an oestrogen-dominated environment.

Evidence for the involvement of a macrophage-derived chemotactic mediator in the neutrophil recruitment induced by staphylococcal enterotoxin B in mice

Staphylococcus aureus secretes enterotoxins which are superantigens and the major cause of food poisoning in man. Staphylococcal enterotoxins types A and B can induce neutrophil migration into the peritoneal cavity of mice through sensory C-fiber neuropeptides, lipoxygenase or cyclooxygenase metabolites, nitric oxide, histamine, platelet-activating factor and resident macrophages. In this work, we examined the influence of macrophage-derived products on neutrophil migration during peritonitis induced by staphylococcal enterotoxin type B (SEB) in mice. Macrophages stimulated with SEB released a thermolabile neutrophil chemotactic protein with a molecular weight of 1,000-3,000 (by ultrafiltration). This release was inhibited 30% by dexamethasone (an inhibitor of cytokine synthesis and phospholipase A(2) activity), but not by indomethacin (a cyclooxygenase inhibitor) or BW755C (a dual cyclo- and lipoxygenase inhibitor). Dexamethasone also inhibited (100%) the neutrophil migration induced by the chemotactic protein. Similar inhibition occurred in mice pretreated with BWA4C (lipoxygenase inhibitor; 90%), BW755C (99%), BN52021 (platelet-activating factor-acether receptor antagonist; 93%), cimetidine (histamine H(2) receptor antagonist; 76%), capsaicin (a depletor of sensory C-fiber neuropeptides; 82%) and the neurokinin-1 receptor antagonist SR140333 (71%), but not by indomethacin or the neurokinin(2) receptor antagonist SR48968. These results confirm that macrophages are involved in the neutrophil recruitment induced by SEB, and that the chemotactic protein apparently induces neutrophil migration by a mechanism mediated by platelet-activating factor, histamine H(2) receptors, lipoxygenase products and substance P.

Estrogen-dependent regulation of neurokinin 3 receptor-mediated uterine contractility in the rat

The receptors for neurokinin 1 (NK1-R), neurokinin 2 (NK2-R), and neurokinin 3 (NK3-R) are expressed and functionally active in the uterus, promoting strong contractions of the myometrium. Previously, we demonstrated that myometrial contractility activated by the NK-Rs is regulated by estrogen. In the current study, we furthered our investigations of the role of estrogen in the regulation of NK3-R-mediated myometrial contractility. Estrogen promotes both heterologous and homologous desensitization of NK3-R-mediated uterine contractility. In tissue obtained from estrogen-dominated rats (ovariectomized estrogen-treated rats and rats in estrus), the magnitude of uterine contractions decreased in response to consecutive additions of the NK3-R-selective agonist senktide. By addition of the fourth dose of agonist, the contractile response was routinely barely above baseline. In contrast, in tissue obtained from non-estrogen-dominated rats consecutive doses of senktide resulted in contractions of identical magnitude. The homologous desensitization was specific to the NK3-R, and the desensitization of the NK3-R-mediated response did not affect the magnitude or nature of uterine contractions in response to NK1-R or NK2-R activation. Furthermore, heterologous and homologous desensitization of NK3-R-mediated contractility is dependent upon the duration of exposure to estrogen. This complex mechanism appears to be important in intact tissue; capsaicin-mediated release of endogenous neuropeptides resulted in a desensitization of response to subsequent stimulation with senktide in estrogen-dominated uterine tissue.

Regional decreases in NK-3, but not NK-1 tachykinin receptor binding in dystonic hamster (dt(sz)) brains

Although the pathophysiology of primary dystonias is currently unknown, it is thought to involve changes in the basal ganglia-thalamus-cortex circuit, particularly activity imbalances between direct and indirect striatal pathways. Substance P, a member of the tachykinin family of neuropeptides, is a major component in the direct pathway from striatum to basal ganglia output nuclei. In the present study quantitative autoradiography was used to examine changes in neurokinin-1 (NK-1) and neurokinin-3 (NK-3) receptors in mutant dystonic hamsters (dt(sz)), a well characterized model of paroxysmal dystonia. NK-1 receptors were labeled in 10 dystonic brains and 10 age-matched controls with 3 nM [(3)H]-[Sar(9), Met(O(2))(11)]-SP. NK-3 binding sites were labeled in adjacent sections with 2.5 nM [(3)H]senktide. NK-1 binding was found to be unaltered in 27 brain areas examined. In contrast, NK-3 binding was significantly reduced in layers 4 and 5 of the prefrontal (-46%), anterior cingulate (-42%) and parietal (-45%) cortices, ventromedial thalamus (-42%) and substantia nigra pars compacta (-36%) in dystonic brains compared to controls. The latter effects may be particularly relevant in view of evidence that activation of NK-3 receptors on dopaminergic neurons in the substantia nigra pars compacta can increase nigrostriatal dopaminergic activity. Since previous studies indicated that a reduced basal ganglia output in mutant hamsters is based on an overactivity of the direct pathway which also innervates substantia nigra pars compacta neurons, the decreased NK-3 binding could be related to a receptor down-regulation. The present finding of decreased NK-3 receptor density in the substantia nigra pars compacta, thalamic and cortical areas substantiates the hypothesis that disturbances of the basal ganglia-thalamus-cortex circuit play a critical role in the pathogenesis of paroxysmal dystonia.

Preprotachykinin A gene expression after administration of 3,4-methylene dioxymethamphetamine (Ecstasy)

This study tested the effects of 8 days of subchronic administration of 3,4-methylene dioxymethamphetamine (MDMA) (5 mg/kg b.w.) on preprotachykinin A mRNA levels in discrete rat brain regions. In situ hybridization examined preprotachykinin A mRNA levels in the core and shell of the nucleus accumbens, the islands of Calleja, the olfactory tubercle, the dorsal and ventral caudate-putamen, the bed nucleus of the stria terminalis, the medial preoptic area, the medial habenular nucleus and in the postero-dorsal part of the medial amygdala. Higher levels of preprotachykinin A mRNA were found in the core and shell of the nucleus accumbens, in the islands of calleja, in the olfactory tubercle, in the bed nucleus of the stria terminalis, in the medial habenular nucleus and the postero-dorsal part of the medial amygdala, compared to control animals. Conversely, increased preprotachykinin A mRNA levels were observed in the dorsal and ventral caudate-putamen in MDMA treated when compared to control rats. In the social memory test, MDMA significantly impaired rats' short-term working memory. These results show that chronic exposure to MDMA strongly affects preprotachykinin A mRNA levels in discrete rat brain regions. These changes occur in experimental conditions in which working memory is markedly reduced, suggesting that changes in gene expression of tachykinin mechanisms may contribute to the effects of MDMA on memory function.

Comparative distribution of NK1, NK2, and NK3 receptors in the rat brainstem auditory nuclei

While the distribution of substance P in the auditory system is well illustrated, the localization of its receptors has not yet been documented. The goal of our study was to characterize the distribution of the tachykinin receptors NK1-R, NK2-R and NK3-R in the brainstem auditory nuclei of the adult rat using immunohistochemical techniques. The immunoreactivity of the neurokinin receptors was found to be widely distributed in most neurons of the cochlear nucleus (CN), the lateral superior olive (LSO), the medial nucleus of the trapezoid body (MNTB) and in the inferior colliculus (IC). Immunoreactivity was generally confined to post-synaptic targets (neuronal cell body and proximal or primary dendrites) in all auditory nuclei. However, unlike brainstem nuclei, the IC showed, in addition to neuronal cell body staining, a positive axonal immunolabeling (axons and pre-synaptic terminals) with the anti-NK1-R antibody. This axonal staining, revealing a pre-synaptic expression of NK1-R, is in good agreement with the known presence of substance P in the IC neurons. The absence of axonal staining in the superior olivary complex nuclei which projects afferent to the IC indicated that the NK1-R labeled axons are rather intrinsic IC fibers or descending thalamic projections to the IC. Overall, the wide distribution of the three types of tachykinin receptors observed in the present study argues for an important role of tachykinin neuropeptides in the central auditory system.

Localization of neurokinin B receptor in mouse gastrointestinal tract

AIM: To observe the location of neurokinin receptor (NK3r) in the mouse gastrointestinal tract.

METHODS: The abdomens of 8 male Kunming mice were opened under anaesthesia with sodium pentobarbital. The exposed gut organs were kept moisture and temperature at the same time. Then the esophagus, jejulum, ileum, colon, etc were respectively cut and the segments from the stomach to the distal colon were opened along the mesenteric border. A circular 4 mm-6 mm enteric part(pieces of 1 cm² were to be prepared) and mucosa and submucosa were removed, then the longitudinal muscle layer was pulled off from the circular muscle layer under microphotograph. They were rinsed in 50 nmol·L^-1 potassium phosphate-buffered saline(PBS). Immunohistochemistry and immunoreactive fluorescence were used in the staining procedures.

RESULTS: There was not NK3r-Like(-Li) positive material on the smooth muscle cells of the esophagus, stomach, and intestines and other regions. The nerve cell bodies with immunoreactivity for NK3r were mainly distributed in the submucousal nerve plexus or myenteric nerve plexus of the gastrointestinal tract except for the esophagus, stomach and rectum. The reaction product was located on the surface of the nerve cell plasma. It was occasionally observed in the cell plasma endosomes, but was very weakly stained. Among the NK3-like positive neurons in the plexus,the morphological type in many neurons appeared like Dogiel II type cells. Some neuron cell bodies were big, having many profiles, some were long ones or having grading structure. Cell body diameter was about 10 μm-46 μm and 8 μm-42 μm in myenteric plexus and submucous plexus.

CONCLUSION: This study not only described the distribution of neurokinin B receptor in the mouse gut in detail, but also provided a morphological basis for deducing the functional identity of the NK3r-LI immunoreactivity neurons, suggesting the possibility that these neurons were closely related to gastrointestinal tract contraction and relaxing activity.

Substance P and nitric oxide signaling in cerebral cortex: anatomical evidence for reciprocal signaling between two classes of interneurons

Parvalbumin-containing fast-spiking interneurons in the cerebral cortex exhibit widespread electrical coupling, as do somatostatin-containing low-threshold spiking interneurons. Besides the classical neurotransmitter gamma-aminobutyric acid, these cortical interneurons may also release various neuropeptides including substance P (SP), as well as the freely diffusible messenger nitric oxide (NO). To investigate whether these two networks of interneurons might interact via these nonclassical messengers, we performed immunocytochemistry for SP and NO signaling pathways in rat somatic sensory cortex. SP was found in a subset of parvalbumin-positive cells concentrated in layers IV and V, whereas its receptor, NK1, was found in a subset of somatostatin-containing neurons (and also, at much lower levels, in a disjoint subset of parvalbumin-containing neurons). Only 4% of SP-containing axon terminals were apposed to NK1-positive dendrites, suggesting that in the cerebral cortex, SP may act predominantly as a paracrine neuromediator. Nitric oxide synthase-I (NOS-I), the synthetic enzyme for NO, was found almost exclusively in NK1-positive neurons; 95% of intensely somatostatin/NK1-positive neurons were also positive for NOS-I, and 94% of NOS-positive neurons were also positive for NK1. Immunoreactivity for soluble guanylyl cyclase (the NO receptor) was at high levels in the apical dendrites of layer V pyramidal neurons and in parvalbumin/SP-positive neurons. These data point to a novel reciprocal chemical interaction between two inhibitory networks in the rat neocortex.

Tachykinin NK(3) receptor agonists induced microvascular leakage hypersensitivity in the guinea-pig airways

Microvascular leakage hypersensitivity is a main component of neurogenic inflammation and of tachykinin effects. The aim of this study was to examine the ability of neurokinin B and of the tachykinin NK(3) receptor agonists, [MePhe(7)]neurokinin B or senktide, to potentiate when given by aerosol the microvascular leakage induced by histamine in guinea-pig airways and to compare their effects to those of tachykinin NK(1) (substance P, [Sar(9),Met(O(2))(11)]substance P) or tachykinin NK(2) (neurokinin A, [betaAla(8)]neurokinin A (4-10)) receptor agonists. Guinea-pigs were pretreated successively for 10 min with aerolized salbutamol and phosphoramidon; 15 min later, they were exposed for 30 min to an aerosolized solution of tachykinin receptor agonists; 24 h later, the animals were anaesthetized and vascular permeability was quantified by extravasation of Evans blue dye. Neurokinin B, [MePhe(7)]neurokinin B and senktide (3 x 10(-6)-3 x 10(-5)M) induced a potentiation of the effects of histamine on the vascular permeability in the trachea and main bronchi. Compared to other tachykinin NK(1) and NK(2) receptor agonists, the order of potency was: senktide>neurokinin B=[Sar(9),Met(O(2))(11)]substance P=[betaAla(8)]neurokinin A (4-10)=[MePhe(7)]neurokinin B>neurokinin A>substance P. The potentiation by [MePhe(7)]neurokinin B of histamine-induced microvascular leakage was abolished by the tachykinin NK(1) receptor antagonist SR140333 ([(S)1-(2-[3-(3,4-dichlorophenyl)-1-(3-iso-propoxyphenylacetyl)piperidin-3-yl]etyl)-4-phenyl-1-azoniabicyclo[2.2.2]octane, chloride]) or the tachykinin NK(3) receptor antagonists SR 142801 ([(R)-(N)-(1-(3-(l-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl) propyl)-4-phenylpiperidin-4-yl)-N-methylacetamide]) and SB 223412 ([(S)-(-)-N-(alpha-ethylbenzyl)-3-hydroxy-2-phenylquinoline-4-carboxamide]). In conclusion, these results suggest that tachykinin NK(3) receptors might be involved in the potentiation of histamine-induced increase in microvascular permeability.

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.

Sources of calcium in neurokinin A-induced contractions of human colonic smooth muscle in vitro

OBJECTIVES

Tachykinins have been implicated in the pathogenesis of colonic dysmotility. The sources of activator calcium for neurokinin A (NKA)-induced contraction of human colonic smooth muscle have not been assessed. We evaluated the contribution of extracellular and intracellular Ca2+ to NKA-induced contractions.

METHODS

Circular smooth muscle strips of human colon were suspended under 1 g of tension in organ baths containing Krebs solution at 37 degrees C gased with 95% O2/5% CO2. Contractile activity was recorded isometrically.

RESULTS

Cumulatively applied NKA (0.1 nmol/L-0.3 micromol/L), produced concentration-dependent contractions of human colonic smooth muscle strips that were not affected by tetrodotoxin (1 micromol/L). The contractile response to NKA was abolished in a Ca2+-free medium containing ethylenediaminetetraacetate (EDTA) (1 mmol/L). Pretreatment of muscle strips with nifedipine (1 micromol/L), an L-type voltage-operated Ca2+ channel antagonist, abolished the contractile responses to NKA. Pretreatment with SK&F 96365 (10 micromol/L and 30 micromol/L), a putative receptor-activated and voltage-operated Ca2+ channel antagonist, attenuated the contractile responses. Depletion of intracellular Ca2+ stores with thapsigargin (1 micromol/L), an inhibitor of the sarcoplasmic reticulum Ca2+ ATP-ase, had no effect on NKA-induced contractions.

CONCLUSIONS

NKA-mediated contraction of human colonic smooth muscle is dependent on an influx of extracellular Ca2+ through L-type voltage-operated Ca2+ channels. Intracellular Ca2+ release seems to have little role to play in NKA-mediated contractions.