Effects of tachykinins on inositol phospholipid hydrolysis in slices of hamster urinary bladder

Tachykinin receptor types: Classification and membrane signalling mechanisms

The use of selective agonists in both functional and binding studies has provided unequivocal evidence for the existence of three types of tachykinin receptor (NK(1), NK(2) and NK(3)); there is also preliminary evidence for the existence of further subtypes. These results have been confirmed by the development of selective antagonists and by the identification and cloning of three distinct cDNA sequences. All three receptors belong to the superfamily of G protein coupled receptors and are linked to the phosphoinositide transmembrane-signalling pathway. The purpose of this article is to review recent developments in the pharmacology of each receptor with emphasis on the NK(3) type. In particular, the need to use selective agonists and antagonists to identify each receptor type is stressed.

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.

Modulation by protein kinase C of the enhanced responsiveness to tachykinins in ovalbumin-sensitized guinea pig alveolar macrophages

As previously reported, alveolar macrophages (AMs) from ovalbumin-sensitized guinea pigs present an enhanced responsiveness to tachykinins but not to N-formylmethionyl-leucyl-phenylalanine (fMLP). We have investigated the biochemical mechanisms underlying this varied responsiveness to tachykinins. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) induced a larger superoxide anion (O2-) production in AMs from sensitized guinea pigs, as did tachykinins. Pretreatment of AMs with pertussis toxin abolished tachykinin-evoked respiratory burst, had no effect on PMA-evoked O2- production and strongly inhibited fMLP-evoked one, with no appreciable variation between control or sensitized AMs. Staurosporine and its derivative cgp 41251, significantly decreased PMA- and tachykinin-evoked O2- production in both populations, being more potent in control AMs, but exerted little effects against fMLP. Pretreatment of AMs with PMA significantly inhibited fMLP-, PMA- and tachykinin-evoked O2- production in both control and sensitized AMs. fMLP, substance P (SP), neurokinin A (NKA) and the NK2 agonist [beta-Ala8]-NKA(4-10) dose-dependently increased [3H] phorbol 12, 13 dibutyrate (PDBu) binding to control and sensitized AMs. While fMLP exerted similar effects in both populations, dose-response curves for SP1 NKA and the NK2 receptor agonist were shifted leftwards (1, 4 and 3 orders of magnitude, respectively) in sensitized AMs. These results indicate a possible PKC involvement in the enhanced responsiveness to tachykinins in actively sensitized AMs.

Neurokinin A and Ca2+ current induce Ca(2+)-activated Cl(-) currents in guinea-pig tracheal myocytes

1. Membrane currents were recorded by a patch clamp technique in guinea-pig tracheal myocytes, using the whole cell mode with Cs(+) internal solution. 2. Both neurokinin A (NKA, 1 mu M) and caffeine (10 mM) evoked Ca(2+)-activated Cl- currents (I[Cl(Ca)]) transiently. In Ca(2+)-free bathing solution, the first application of NKA or caffeine elicited I[Cl(Ca)] but the second application of these substances failed to activate it. In addition, pretreatment with ryanodine in the presence of caffeine abolished the response to both NKA and caffeine whilst heparin (200 mu g ml(-1)) only blocked the NKA-induced response. I[Cl(Ca)] was also elicited by inositol 1,4,5-trisphosphate (IP(3)). 3. Command voltage pulses positive to 0 mV from a holding potential of -60 mV activated the voltage-dependent L-type Ca2+ current (I(Ca,L)) and late outward current. Upon repolarization to the holding potential, slowly decaying inward tail currents were recorded. The outward current during the depolarizing pulses and the inward tail current were enhanced by Bay K 8644, but completely blocked by Cd2+ or nifedipine. Replacement of external Ca2+ with Ba2+, removal of Ca2+ from the bath solution, or inclusion of EGTA (5 mM) in the patch pipette, also led to abolition of these currents, indicating that they were Ca2+ dependent, and that Ca2+ influx due to I(Ca,L) activated the currents. 4. When [Cl(-)](O) or [Cl(-)](i) was changed, the reversal potential (E(rev)) of the Ca2+-activated currents shifted, thus behaving like a Cl(-)-selective ion channel as predicted by the Nernst equation. DIDS (1 mM) completely abolished the currents, also suggesting that they were I[Cl(Ca)]. 5. NKA (1 mu M) and caffeine (30 mM) transiently activated I[Cl(Ca)], and after that both agents markedly reduced I[Cl(Ca)] induced by I(Ca,L). This is probably due to sarcoplasmic reticulum (SR) Ca2+ release induced by NKA or caffeine, followed by inhibition of the Ca(2+)-induced Ca2+ release from the SR. 6. The present results indicate that I[Cl(Ca)] can be activated by SR Ca2+ release due to NKA or caffeine (through IP(3) or ryanodine receptors) as well as by Ca2+ influx due to I(Ca,L). It also suggests that activation of I[Cl(Ca)] by NKA may be mediated by the production of IP(3), which releases Ca2+ from the SR.

Tachykinins alter inositol phosphate formation, but not cyclic AMP levels, in primary cultures of neonatal rat spinal neurons through activation of neurokinin receptors

The naturally occurring tachykinins, substance P, neurokinin A and neurokinin B, induce the formation of inositol phosphates or cAMP in a variety of tissues but their effects on neurons have not been resolved. We used primary cultures of neonatal rat spinal cord to determine whether neurokinin receptors mediate changes in these second messengers in spinal neurons. We found that substance P, neurokinin A and neurokinin B induced the formation of inositol phosphates in a concentration-dependent manner with similar potencies (EC50S: 3.6, 5.7 and 21.3 nM, respectively), but at concentrations tested (0.1-1.0 microM) these peptides had no effect on cAMP levels. All three tachykinins induced the formation of inositol phosphates predominately by activation of neurokinin1 receptors. CP-96,345 and WIN 51,708, neurokinin1 receptor antagonists, attenuated the response to substance P, neurokinin A and neurokinin B. GR 103,537, a neurokinin2 receptor antagonist, had no effect on the responses induced by any of the tachykinins. Furthermore, the selective neurokinin1 receptor agonist, GR-73632, induced the formation of inositol phosphates in a concentration-dependent manner, whereas the selective neurokinin2 receptor agonist, GR-64349, generated inositol phosphates only at the highest concentration tested (10 microM). Senktide, a neurokinin3 receptor agonist, did not induce the formation of inositol phosphates at any of the concentrations tested (0.01-10 microM). Inositol phosphate formation appeared to be due to a direct effect of the tachykinins on neuronal neurokinin1 receptors. These results suggest that biological responses in spinal neurons following activation of neurokinin1 receptors are mediated mainly by the hydrolysis of phosphoinositol 4,5-bisphosphate to form inositol 1,4,5-trisphosphate and diacylglycerol. It remains to be determined which of these second messengers mediates the increased neuronal excitability and depolarization that occurs in response to substance P.

Ionic basis of neurokinin-A-induced depolarization in single smooth muscle cells isolated from guinea-pig trachea

Neurokinin A (NKA) caused single tracheal smooth muscle cells (TSMCs) to contract. The effects of NKA on the electrical activity of guinea-pig TSMCs were examined using the tight-seal whole-cell patch-clamp technique. Under current-clamp conditions at rest, the membrane potential of TSMCs spontaneously oscillated at about -40 mV and NKA rapidly depolarized the membrane potential to nearly 0 mV, which then gradually repolarized to about -20 mV in the presence of NKA. The oscillations in potential disappeared transiently during the rapid phase of depolarization in response to NKA and reappeared during the sustained phase of depolarization. Under voltage-clamp conditions, NKA evoked an inward current which faded quickly. Subsequently, the cell conductance in the presence of NKA at potentials greater than -40 mV decreased gradually. The reversal potential of the NKA-induced inward current was about 0 mV, and shifted with changes in the Cl- equilibrium potential. The Cl- current was not elicited by NKA when using a pipette solution containing 10 mM ethylenebis(oxonitrilo)tetraacetic acid (EGTA). During the sustained phase, K+ currents evoked by depolarizing voltage steps were inhibited by NKA. The present results indicate that NKA causes rapid and sustained depolarization of TSMCs by two distinct mechanisms: (1) initial transient activation of the Ca(2+)-dependent Cl- current, and (2) sustained inhibition of K+ currents.

Bradykinin B1 receptors in the rabbit urinary bladder: induction of responses, smooth muscle contraction, and phosphatidylinositol hydrolysis

1. The aim of this study was to analyse the pharmacological characteristics, and second-messenger coupling-mechanisms, of bradykinin B1 receptors in an intact tissue, the rabbit urinary bladder; and to investigate the influence of inhibition of endogenous peptidases on kinin activities. 2. In preparations of rabbit mucosa-free urinary bladder, at 90 min after mounting of the preparations, bradykinin (1 nM-10 microM) evoked contractile responses. In contrast, the B1 receptor-selective agonist [des-Arg9]-BK (10 mM-10 microM) was only weakly active at this time. Contractile responses to [des-Arg9]-BK increased with time of tissue incubation in the organ bath, reaching a maximum after 3 h, when the pD2 estimates were 6.4 +/- 0.3 for bradykinin, and 6.9 +/- 0.2 for [des-Arg9]-BK. 3. Once stabilized, responses to [des-Arg9]-BK in the bladder were competitively antagonized by the B1 receptor-selective antagonists [Leu8,des-Arg9]-BK and D-Arg-[Hyp3,Thi5,D-Tic7,Oic8,des-Arg9]-BK ([des-Arg10]-Hoe140) (pKB estimates were 6.1 +/- 0.1 and 7.1 +/- 0.1, respectively; n = 17-21), but responses were unaffected by the B2 receptor-selective antagonist D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe140) (100 nM; n = 4). Contractile responses to bradykinin itself were partially, but significantly, inhibited by the B1 receptor-selective antagonist, [Leu8,des-Arg9]-BK (10 microM) (P < 0.05), or by the B2 receptor-selective antagonist Hoe140 (100 nM) (P < 0.005) alone, and were largely blocked by a combination of the two antagonists (P < 0.0001). 4. The combined presence of the carboxypeptidase inhibitor DL-2-mercaptomethyl-3-guanidinoethylthiopropanoicacid (mergetpa; 10 microM), the neutral endopeptidase inhibitor, phosphoramidon (1 microM),and the angiotensin-converting enzyme inhibitor, enalaprilat (1 microM) increased the potency of bradykinin17 fold (P<0.001), but that of [des-Argl-BK was unchanged (P>0.05): pD2 estimates were 7.6 +/- 0.1 and 6.8 +/- 0.1 for bradykinin and [des-Argl-BK, respectively, in treated preparations. In the presence of peptidase inhibitors, the affinities of the antagonists [Leu8,des-Arg9]-BK and [des-Arg'j-Hoel4O were unchanged as compared with those determined in the absence of peptidase inhibitors (P> 0.05).[Leu8,des-Argj-BK inhibited responses to bradykinin under these conditions (n = 4).5. In endothelium-denuded preparations of the rabbit isolated aorta, an archetypal B1 receptor preparation,contractile responses to the B1 receptor-selective agonist [des-Argl-BK (10nM- 1O0 AM) (and to bradykinin) increased progressively with time of tissue incubation; and [des-Argl-BK responses were completely antagonized by the B. receptor antagonist [Leu8,des-Arg9]-BK (pKB 6.3 +/- 0.2; n = 13).6. In experiments measuring stimulation of hydrolysis of phosphatidylinositol in rabbit urinary bladder,[des-Argl-BK (10 microM- 1 mM), and bradykinin (100 microM) significantly increased accumulation of inositol phosphates (P<0.0001). The increase in accumulation of inositol phosphates evoked by [des-Arg9]-BK(10 microM - 1 mM) was significantly inhibited by [des-Arg'j-Hoe 140 (10 microM) (P <0.01).7. We conclude that in the mucosa-free rabbit urinary bladder, [des-Argl-BK evokes contraction largely via activation of B1 receptors which have similar properties, including time-dependent induction,to B1 receptors in the rabbit isolated aorta. Bradykinin evokes contraction via stimulation of both B1 and B2 receptors, but does not require conversion by peptidases in order to activate B1 receptors. We demonstrate, for the first time, B1 receptor-coupling to phosphatidylinositol hydrolysis in an intact tissue preparation.

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.

Parainfluenza virus type 3 induced alterations in tachykinin NK1 receptors, substance P levels and respiratory functions in guinea pig airways

We have investigated the effects of parainfluenza virus type 3 (PI-3) on sensory neuropeptide levels, tachykinin receptors and their functions in guinea pig airways during the course of respiratory viral infection. PI-3 infected guinea pigs were hyperresponsive to methacholine and substance P aerosols as determined by earlier onset of dyspnea in these animals as compared with control on post-inoculation day (PID) 7 but not 19. In addition, plasma protein extravasation produced in response to the tachykinin was increased in infected airways during the first week post inoculation. Infected guinea pig trachea did not respond any differently to methacholine when smooth muscle contraction and [3H]inositol phosphate accumulation were measured although the magnitude of substance P effects using in vitro tests was significantly greater than control on post-inoculation day 7 but not 19. Trachea from PI-3 infected animals were characterized by reductions in substance P-like immunoreactivity, tachykinin NK1 receptor number and agonist affinity during the first post-inoculation week. Substance P levels or tachykinin NK1 receptor numbers or affinity were not altered in trachea of guinea pigs 4 days after treatment with lipopolysaccharide. These data suggest substance P release occurs during critical periods of respiratory viral infection which are temporally correlated with airway hyperresponsiveness. Despite apparent down-regulation of tachykinin NK1 receptors, substance P-mediated functions remained enhanced suggesting some alterations in post-receptor mechanisms.

Evidence for a role of protein kinase C in the sustained activation of rat dorsal horn neurons evoked by cutaneous mustard oil application

The intracellular mechanisms involved in the sensitisation of spinal dorsal horn neurons brought about by sustained or repeated nociceptive inputs are unknown. The present experiments addressed any role of protein kinase (PKC) in sustained nociceptive responses of rat dorsal horn neurons by: (i) ionophoretic administration of PKC inhibitors whilst recording activity evoked by repeated cutaneous application of mustard oil; and (ii) assessing subcellular translocation of PKC evoked in spinal cord by cutaneous application of mustard oil. Both marked attenuation of mustard oil-induced neuronal activity by PKC inhibitors and selective translocation of PKC in spinal cord tissue ipsilateral to mustard oil application strongly supported a critical role of PKC in sustained nociceptive responses to mustard oil.

Effects of tachykinins on phosphoinositide metabolism in the hypothalamus: is the NK1 receptor involved?

Substance P (SP) has been shown to stimulate the hydrolysis of inositol phospholipids in peripheral tissues and in the brain. In mammalian peripheral tissues, three tachykinin receptor subclasses, neurokinin 1 (NK1), neurokinin 2 (NK2) and neurokinin 3 (NK3), have been identified. The purpose of our study was to pharmacologically characterize the SP receptors in the hypothalamus using phosphoinositide breakdown as a functional response. SP, previously described as a NK1 agonist, and Neurokinin A (NKA), previously described as a NK2 agonist, stimulated phosphoinositide breakdown in the hypothalamus in a dose-dependent fashion, with SP being more potent than NKA. The NK2-selective antagonist L-659,877, at a dose of 10(-6) M, abolished the effect of SP (10(-8) M) without affecting basal phosphoinositide breakdown. However, this NK2-selective antagonist did not inhibit the NKA-induced stimulation in phosphoinositide metabolism. The NK1-selective antagonist L-668,169 stimulated phosphoinositide metabolism at a concentration of 10(-6) M, but not at 10(-8) M. This NK1-receptor antagonist did not significantly inhibit the effect of SP on phosphoinositide metabolism. Spantide II, another NK1-selective antagonist, also stimulated phosphoinositide metabolism at a dose of 10(-6) M. Like L-668,169, spantide II failed to inhibit the SP-induced stimulation of phosphoinositide metabolism, and even potentiated the response to SP.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Signal transduction mechanisms of recombinant bovine neurokinin-2 receptor stably expressed in baby hamster kidney cells

The bovine neurokinin-2 (NK-2) receptor gene was stably transfected into Baby hamster kidney (BHK-21) fibroblasts and one recombinant clone expressing 17,700 high-affinity [125I]neurokinin A (NKA) binding sites/cell characterized further. [125I]NKA binding was displaced by unlabeled NKA with an IC50 of 8.26 +/- 2 nM (n = 5) and with the rank order of potency NKA > neurokinin B (NKB) > Substance P (SP) confirming pharmacological characteristics of an NK-2 receptor subtype. Stimulation with NKA resulted in a rapid and dose-dependent increase in inositol 1,4,5-trisphosphate (IP3) levels (EC50 = 32 +/- 10 nM; n = 7) which was paralleled by a transient biphasic rise in intracellular free calcium concentration [Ca2+]i (EC50 = 35 +/- 20 nM; n = 3). In addition to phosphoinositide (PI) hydrolysis and Ca2+ mobilization, NKA was found to stimulate both cyclic AMP formation (EC50 = 1.02 +/- 0.26 microM; n = 7) and [3H]arachidonic acid mobilization (EC50 = 0.65 +/- 0.45 microM; n = 4). Interestingly, cyclic AMP levels also rose after addition of an exogenous arachidonic acid metabolite, prostaglandin E2 (PGE2) (EC50 = 11.5 +/- 2 microM). Similar observations of NKA-induced IP3 production, Ca2+ mobilization, arachidonic acid liberation, and cAMP formation have been made previously following expression of the bovine NK-2 receptor in Chinese hamster ovary (CHO) epithelial cells. The present results suggest that activation of NK-2 receptors leads to characteristic and reproducible intracellular second messenger responses in a subclass of cell types which includes fibroblasts and epithelial cells irrespective of their genetic and phenotypic background.

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.

Non-peptide antagonists, CP-96,345 and RP 67580, distinguish species variants in tachykinin NK1 receptors

1. The potency of the non-peptide antagonists CP-96,345 and RP 67580 on NK1 receptor-stimulated [3H]-inositol phosphate accumulation in cell lines or tissue from three different species has been examined. 2. We have used: UC11 cells, derived from a human astrocytoma, and rat LRM55 glial cells, both of which express large numbers of functional NK1 receptors, and the well characterized guinea-pig ileum which expresses both NK1 and NK3 receptors. 3. RP 67580 has an approximately 25 fold lower affinity for NK1 receptors in human UC11 cells (Kd = 194 nM) than in rat LRM55 cells (Kd = 7.9 nM), in contrast CP-96,345 has an approximately 200 fold lower affinity in rat LRM55 cells (Kd = 210 nM) relative to human UC11 cells (Kd = 0.99 nM). The pharmacological profile of CP-96,345 and RP 67580 in guinea-pig ileum was similar to that observed in human UC11 cells. 4. In conclusion, we have demonstrated that previously reported species differences in binding affinities for the non-peptide NK1 antagonists, CP-96,345 and RP 67580, are also observed in inhibition of NK1 receptor stimulated hydrolysis of inositol phospholipids.

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

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

Neurokinin A-stimulated phosphoinositide breakdown in rabbit iris sphincter muscle

Specific [3H]-substance P binding was saturable and of high affinity (KD = 2.5 nM) with a Bmax of 725 fmol/mg protein in the isolated rabbit iris sphincter muscle. The competition for [3H]-substance P binding was in the order of eledoisin greater than substance P greater than kassinin greater than neurokinin B greater than neurokinin A greater than physalaemin. In the same preparation, neurokinin A, as well as substance P induced a concentration-related accumulation of [3H]-inositol phosphates (IPs), and the maximum increase was about 200% of the control at 10(-4) M. [D-Arg1, D-Trp7,9, Leu11]-substance P (SP) and [D-Pro2, D-Trp7,9]-SP (10(-3) M) inhibited substance P or neurokinin A (10(-4) M)-induced phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis significantly. [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP (10(-3) M) also inhibited neurokinin A (10(-4) M)-induced PIP2 hydrolysis significantly. Neurokinin A and substance P produced concentration-related contractions in normal Ca(2+)-containing medium. The contractile response was weaker in Ca(2+)-free medium, and there was no response in 0.2 mM EGTA medium. In Ca(2+)-free medium, the basal level of [3H]-IPs accumulation was smaller than that in normal medium, and neurokinin A and substance P significantly increased PIP2 hydrolysis. In the 0.2 mM EGTA containing medium, neurokinin A and substance P did not stimulate the PIP2 hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Comparison of the effects of neuropeptide K and neuropeptide gamma with neurokinin A at NK2 receptors in the hamster urinary bladder

Neuropeptide K (NPK) and neuropeptide gamma (NP gamma) are two endogenous N-terminally extended forms of neurokinin A (NKA). Here, we compared their effects with those of NKA on 125I-NKA binding, phosphatidylinositol (PI) turnover and smooth muscle contraction in the hamster urinary bladder. NPK, NP gamma and NKA were equipotent in competing 125I-NKA from NK2 receptors in crude hamster bladder membranes. All three peptides stimulated PI turnover by approximately 750% with similar potency. In a third series of experiments, these peptides had similar efficacy in inducing a dose-dependent contraction of bladder smooth muscle. The NK2 receptor selective antagonist L-659,877 (cyclo[Leu-Met-Gln-Trp-Phe-Gly]) inhibited the stimulation of PI turnover and bladder contractions induced by all three tachykinins. The present results show that NKA, NPK and NP gamma display a similar biological profile. The N-terminal extensions of NPK and NP gamma appear not to influence binding of these peptides to NK2 receptors, NK2 receptor mediated stimulation of PI turnover, or smooth muscle contraction in hamster urinary bladder.

Pharmacological specificity of novel, synthetic, cyclic peptides as antagonists at tachykinin receptors

1. The interaction at tachykinin receptors of a series of novel cyclic hexapeptides has been examined by use of radioligand binding assays (NK1 and NK3 sites in rat cortex, NK2 sites in hamster urinary bladder) and functional pharmacological assays (guinea-pig ileum, rat vas deferens and rat portal vein for NK1, NK2 and NK3 receptors, respectively). 2. The compounds cyclo(GlnTrpPhe(R)Gly[ANC-2]LeuMet) (L-659,837) and cyclo(GlnTrpPheGly-LeuMet) (L-659,877) were powerful and selective displacers of NK2 binding (pIC50 6.9 and 8.0, respectively), and were competitive antagonists of responses to stimulation of NK2 receptors in rat vas deferens (pKB for antagonism of responses to eledoisin 6.7 and 8.1, respectively). Responses in the NK1 and NK3 pharmacological assays were blocked only weakly, if at all. 3. In the longitudinal muscle of the small intestine of the rat, responses to stimulation of the putative NK2 receptor by eledoisin, neurokinin A or neurokinin B were antagonized by both cyclo(GlnTrpPhe(R)-Gly[ANC-2]LeuMet) and cyclo (GlnTrpPheGlyLeuMet) in a manner consistent with the presence in this tissue of a uniform population of receptors, indistinguishable from the NK2 receptor of the rat vas deferens. 4. The compounds cyclo(GlnTrpPheGlyLeuMet) and the lactam-containing analogue are among the most selective antagonists for the NK2 receptor that have been described; their availability should be of value in the characterization of the receptors mediating responses to tachykinins, and in elucidating the physiological functions of the tachykinin receptors.

Substance P modulates the time course of nicotinic but not muscarinic catecholamine secretion from perfused adrenal glands of rat

1. Substance P (SP) and acetylcholine (ACh) are contained within the splanchnic nerve terminals in the adrenal gland and can be released in response to stress. In the rat, the release of aCh brings about secretion of catecholamines (CA) by acting on nicotinic and muscarinic receptors on the adrenal chromaffin cells. 2. In the present study, we have used a rat isolated adrenal gland preparation to investigate the effects of SP, perfused at different concentrations, on CA secretion evoked by 10(-5) M nicotine and 10(-4) M muscarine. 3. In the first 10 min stimulation period (S1), in the absence of SP, nicotine (10(-5) M) evoked substantial and equal secretion of noradrenaline (NA) and adrenaline (Ad). In a second 10 min stimulation period (S2), carried out 18 min after S1, the nicotinic response was desensitized. In contrast, the muscarinic response, which preferentially evoked Ad secretion in S1 (Ad/NA: 8.7/1), was well maintained in S2. 4. SP present in S1 had no effect on desensitization of the subsequent nicotinic response in S2. 5. At low concentrations (10(-7)-10(-10) M), SP changed the time course of nicotine-induced CA secretion during S1 by enhancing CA secretion in the first 4 min and inhibiting CA secretion thereafter. The maximal effect occurred at 10(-9) M SP. 6. At a higher concentration (10(-5) M), SP inhibited total nicotinic CA secretion throughout S1 and produced a biphasic secretion of CA (depressed in the presence of SP and enhanced after wash out of SP). Pre-exposure of adrenal glands to SP (10-' to 10- M) for 10min produced marked inhibition of the nicotine-induced CA secretion. 7. In contrast to the effect of SP on the nicotinic response, SP from 10- to 10-SM had no effect on muscarinic CA secretion. 8. This difference in sensitivity of the nicotinic and muscarinic responses to SP points to a diversity of mechanisms available for control of adrenal catecholamine secretion. In addition to the ability of SP to increase or decrease the total amount of adrenal CA secretion, dependent on the concentration of SP, the present study shows that SP can change the time-course of nicotinic CA secretion. These results with the rat adrenal gland perfused in vitro suggests both a quantitative and temporal role for SP as a novel modulator of adrenal CA secretion.

Subtypes and excitation-contraction coupling mechanisms for neurokinin receptors in smooth muscle of the guinea-pig Taenia caeci

This study investigated the subtype and coupling mechanisms mediating the direct contractile response to tachykinins in the guinea-pig Taenia caeci preparation in vitro. Coupling of neurokinin receptors was compared throughout with coupling of muscarinic receptors. The smooth muscle neurokinin receptors seem to be predominantly of the NK-1 subtype. Thus, the relative activities of the common naturally-occurring tachykinins fell within one order of magnitude, and the selective NK-1 receptor agonist substance P methyl ester was high in activity (0.38 relative to substance P). Some contribution from NK-3 receptors is, however, possible in view of the appreciable activity of the selective NK-3 agonist succ-[Asp6, N-MePhe8]-SP(6-11) (senktide; activity 0.004 relative to substance P), and NK-2 or NK-3 receptors in view of the higher activity of the D-isomer of [Glp6, *Pro9]-SP(6-11) as compared to its NK-1 selective L-isomer (D/L-activity ratio 1.53). Contractile actions of tachykinins were compared with carbachol for reliance on membrane-potential dependent (electromechanical) and membrane-potential independent (pharmacomechanical) coupling mechanisms. Log concentration-response curves to carbachol and substance P in normal Krebs' medium were compared with curves obtained in a high-K+ solution where processes dependent on changes in membrane potential could play no part in excitation. In the high-K+ depolarizing solution, a concentration-related relationship was maintained, though with some diminution in the maximal additional tension generated: the maximum tension with carbachol was under both conditions greater than that with substance P. The relative effects of several tachykinins and carbachol in producing receptor-mediated changes in membrane permeability through presumed receptor-operated ion channel opening, was estimated in terms of the ability to increase 86Rb-efflux, as a marker for K+, in a high-K+ depolarizing solution. Carbachol (10 microM) consistently increased 86Rb-efflux. In contrast, no permeability increase could be detected with any tachykinin tested (substance P, eledoisin, substance P methyl ester, neurokinin A, neurokinin B, 1 or 10 microM). Tachykinins and carbachol were compared in terms of ability to increase phosphatidylinositol hydrolysis. Both substance P and carbachol showed a concentration-related increase in accumulation of total inositol phosphates; though the maximal response to carbachol was considerably greater than that to any tachykinin (substance P, eledoisin, substance P methyl ester, senktide, neurokinin A, neurokinin B), or combination of two tachykinins (substance P and eledoisin, senktide and substance P methyl ester).(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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.

Characterization of the murine pancreatic receptor for gastrin releasing peptide and bombesin

The murine pancreatic receptor for bombesin and gastrin releasing peptide (GRP) has been characterized. Analysis of the binding of 125I-GRP to membranes indicates a single class of sites (10(-13) mol/mg protein) with Kd of 43 pM. A 70 kDa membrane protein was cross-linked to 125I-GRP by bis(sulfosuccinimidyl) suberate; labeling was blocked by GRP, GRP (14-27), AcGRP(20-27), GRP(18-27), bombesin and ranatensin, was partially blocked by [Leu13 psi (CH2NH)Leu14]bombesin and was unaffected by GRP(21-27) and GRP(1-16). The IC50 values for the competitive displacement of 125I-GRP from intact membranes by these peptides were similar to those obtained by the cross-linking experiments showing that the 70 kDa protein is the GRP receptor. The GRP receptor is G-protein coupled; divalent cations are required for high-affinity binding and nonhydrolyzable GTP analogs decrease receptor affinity. In minced pancreas, GRP caused a dose-dependent increase in inositol phosphates implicating phospholipase C in signal transduction. We suggest that the murine pancreatic receptor for bombesin/GRP is a 70 kDa membrane protein, is associated with a G-protein and stimulates phosphatidylinositol turnover.

Novel selective agonists and antagonists confirm neurokinin NK1 receptors in guinea-pig vas deferens

1. This study investigated the recognition characteristics of neurokinin receptors mediating potentiation of the contractile response to field stimulation in the guinea-pig vas deferens. 2. A predominant NK1 receptor population is strongly suggested by the relative activities of the common naturally-occurring tachykinin agonists, which fall within less than one order of magnitude. This conclusion is supported by the relative activities of the synthetic NK1 selective agonists substance P methyl ester, [Glp6,L-Pro9]-SP(6-11) and delta-aminovaleryl-[L-Pro9,N-MeLeu10]- SP(7-11) (GR73632) which were 0.78, 9.3 and 120 as active as substance P, respectively. Furthermore, the NK2 selective agonist [Lys3, Gly8,-R-gamma-lactam-Leu9]-NKA(3-10) (GR64349) was active only at the highest concentrations tested (greater than 10 microM), and the NK3 selective agonist, succ-[Asp6,N-MePhe8]-SP(6-11) (senktide) was essentially inactive (10 nM-32 microM). 3. [D-Arg1,D-Pro2,D-Trp7,9,Leu11]-SP(1-11) antagonized responses to neurokinin A, neurokinin B, physalaemin, eledoisin, [Glp6,D-Pro9]-SP(6-11), GR73632 and GR64349 (apparent pKB s 5.6-6.2), but was less potent in antagonizing responses to substance P, substance P methyl ester and [Glp6,L-Pro9]-SP(6-11) (apparent pKB s less than or equal to 5.0-5.0). 4. In contrast, the recently developed NK1-selective receptor antagonist [D-Pro9[Spiro-gamma-lactam]Leu10,Trp11]-SP(1-11) (GR71251) did not produce agonist-dependent pKB estimates. Schild plot analysis indicated a competitive interaction with a single receptor population where the antagonist had an estimated overall pKB of 7.58 +/- 0.13 for the four agonists of differing subtype selectivity tested (GR73632, GR64349, substance P methyl ester and neurokinin B). This estimate is similar to that we obtained for NK1-mediated (substance P methyl ester) contraction in the guinea-pig ileum preparation (pKB= 7.86+ 0.05). 5. Tachykinin action appears not to depend on release of a number of intermediary mediators including acetylcholine, histamine or cyclo-oxygenase products, nor to involve interaction with neuronal mechanisms including alpha 2-adrenoceptor feedback, noradrenergic Uptake-I or opioid-release, since antagonism or inhibition of these mechanisms did not modify responses to tachykinins. 6. We conclude that tachykinin action in the field-stimulated guinea-pig vas deferens preparation is mediated through interaction with a predominant neurokinin NK, receptor population and this preparation can therefore be used to study NK, modulation of sympathetic neurotransmission.

Pharmacological characterization of tachykinin-stimulated inositol phospholipid hydrolysis in peripheral tissues

1. Tachykinin-stimulated inositol phospholipid hydrolysis was examined in slices of rat parotid gland, hamster urinary bladder and guinea-pig ileum longitudinal muscle. 2. In the presence of lithium, substance P and other naturally-occurring and synthetic tachykinins induced large, dose-dependent increases in [3H]-inositol monophosphate accumulation. 3. In slices of rat parotid gland, [pGlu6,L-Pro9]SP(6-11) was considerably more potent in stimulating inositol phospholipid hydrolysis than [pGlu6,D-Pro9]SP(6-11). 4. In contrast, in slices of hamster urinary bladder, [pGlu6,D-Pro9]SP(6-11) exhibited greater potency in evoking inositol phospholipid breakdown than [pGlu6,L-Pro9]SP(6-11). 5. The differential selectivity of these C-terminal fragments of substance P suggests that they may be useful tools for distinguishing between NK1 and NK2 receptors. 6. L-659,837 and L-659,874 antagonized eledoisin-stimulated inositol phospholipid hydrolysis in slices of hamster urinary bladder. Neither compound significantly reduced substance-P evoked inositol phospholipid breakdown in slices of rat parotid gland, or senktide-induced inositol phospholipid hydrolysis in slices of guinea-pig ileum. 7. L-659,837 and L-659,874 had no effect on the atropine-sensitive, carbachol-stimulated inositol phospholipid hydrolysis in slices of rat parotid gland. 8. These data further support the notion that L-659,837 and L-659,874 are potent and selective NK2 receptor antagonists.

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.

[Leu9 psi(CH2NH)Leu10]-neurokinin A (4-10) (MDL 28,564) distinguishes tissue tachykinin peptide NK2 receptors

The neurokinin A analogue, MDL 28,564 (Asp-Ser-Phe-Val-Gly-Leu-CH2NH-Leu-NH2), inhibited 125I-NKA binding to hamster urinary bladder NK2 receptors with a KI of 130 nM. For rat submaxillary gland NK1 receptors and cerebral cortical NK3 receptors, the KI's for MDL 28,564 were greater than 250 microM and greater than 500 microM, respectively. MDL 28,564 did not relax dog carotid artery (NK1 tissue) or contract rat portal vein (NK3 tissue). In guinea-pig trachea tissues, MDL 28,564 stimulated phosphatidylinositol turnover and induced contraction with maximum effects similar to those of neurokinin A. In hamster urinary bladder tissue, MDL 28,564 stimulated phosphatidylinositol turnover with maximum effect only 10% of that of neurokinin A, did not produce sustained contraction itself and antagonized NKA-induced contraction. MDL 28,564 also produced full contraction in rabbit pulmonary artery (NK2 tissue) but was inactive in rat vas deferens (NK2 tissue). These data with MDL 28,564 are consistent with the NK2 receptors in guinea-pig trachea and rabbit pulmonary artery being different from those in hamster urinary bladder and rat vas deferens.

NK-1 receptor mediation of neurogenic plasma extravasation in rat skin

1. Plasma extravasation was induced by electrical nerve stimulation and by perfusion of tachykinins over a vacuum-induced blister base on rat footpad. 2. Stimulation of the sciatic nerve (18 V, 15 Hz, 0.5 ms) for 20 min produced a significant increase in the protein content of the perfusate. The response in capsaicin pretreated rats was only 4% of the control response. This indicates that the electrically-induced plasma extravasation response was mediated by capsaicin-sensitive sensory fibres. 3. Exogenous perfusion of the mammalian tachykinins substance P, neurokinin A and neurokinin B and the non-mammalian tachykinins physalaemin, kassinin and eledoisin was used to determine the tachykinin receptor type mediating the plasma extravasation response. Dose-response curves of the tachykinins (10(-9) M-10(-4) M) gave a rank order of potency of substance P = physalaemin greater than eledoisin greater than or equal to kassinin greater than neurokinin B = neurokinin A. 4. In addition, specific agonists of neurokinin receptors were perfused. Perfusion of [Glp6, D-Pro9] SP6-11 and [Glp6, L-Pro9]SP6-11 demonstrated that the L-Pro isomer was much more potent than the D-Pro isomer. 5. The rank order of potency and the greater potency of [Glp6, L-Pro9]SP6-11 over its D-isomer indicate an NK-1 neurokinin receptor mediates plasma extravasation in rat footpad skin.

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.

Substance P induced hydrolysis of inositol phospholipids in rat skin in an in vivo model of inflammation

The present study was undertaken to study the ability of substance P (SP) to induce inositol phospholipid (IP) hydrolysis measured as inositol mono-phosphate (IP1) accumulation, in an in vivo blister model of neurogenic inflammation in the rat hind footpad. SP was found to induce IP1 accumulation in a concentration dependent manner. The use of SP analogues (SP5-11 and SP1-7) indicated that the response is mainly mediated by the C-terminal sequence of the peptide. The response was significantly reduced by the SP antagonist spantide, suggesting that the response is mostly due to activation of the SP receptor on small diameter vessels. Capsaicin pretreatment did not have an effect on the ability of SP to induce the response. Experiments with mepyramine suggest that the response is also partly mediated by SP induced histamine release from mast cells. This is the first study to provide direct evidence for phosphoinositide mediated SP effects in the skin.

Novel autonomic neurotransmitters and intestinal function

A wide variety of substances, including amines and peptides, have been detected within the complex neuronal pathways of the enteric nervous system using immunohistochemical techniques. In this article we have discussed some of the more recent data on the effects of these substances on intestinal activity. We have also commented on the many difficulties associated with ascribing neurotransmitter status to individual compounds. The technique of immunoblockade of neurogenic functional responses has been used in an attempt to identify some of the putative neurotransmitter substances. The search for selective antagonists continues.

The effect of substance P and other tachykinins on inositol phospholipid hydrolysis in rabbit retina, superior colliculus and retinal cultures

Substance P and eledoisin stimulate the accumulation of inositol phosphates in a dose-dependent manner in retinal and superior colliculus slices of the rabbit. The EC50 values for substance P and eledoisin in both tissues were of the same order (1.5-4.9 microM), suggesting that the receptors in the two tissues were alike with characteristics of the SP-P subtype rather than the SP-E subtype. These data suggest that the SP-immunoreactive material in the retinal ganglion and amacrine cells is identical. The effectiveness for a number of tachykinin substances at 10(-5) M for stimulating inositol phosphates accumulation was as follows: Substance P greater than eledoisin greater than neurokinin A greater than neurokinin B greater than substance P (octapeptide) greater than substance P (pentapeptide). Spantide [(D-Arg1, D-Try7.9, Leu11) substance P] and (D-Pro2, D-Try7.9) substance P did not stimulate inositol phospholipid hydrolysis. However, spantide, at a concentration of 10(-6) M, was an antagonist of the effect produced by substance P, but had no action on the effect produced by neurokinin A or neurokinin B. Substance P and other tachykinins were also effective in stimulating inositol phosphates accumulation in 3-5-day-old rabbit retinal cultures but did not elicit a response in the older (25-30-day-old) cultures which lacked neurones but contained Müller cells. Furthermore, substance P was only active in the younger cultures in stimulating an increase in internal calcium levels. It is therefore concluded that retinal tachykinin receptors linked to phosphoinositide turnover and calcium mobilisation are associated exclusively with neurones and not with Müller cells.