Inositol 1,4,5-trisphosphate-gated calcium transport through plasma membranes in nerve terminals

Prothymosin α Plays Role as a Brain Guardian through Ecto-F1 ATPase-P2Y12 Complex and TLR4/MD2

Prothymosin alpha (ProTα) was discovered to be a necrosis inhibitor from the conditioned medium of a primary culture of rat cortical neurons under starved conditions. This protein carries out a neuronal cell-death-mode switch from necrosis to apoptosis, which is, in turn, suppressed by a variety of neurotrophic factors (NTFs). This type of NTF-assisted survival action of ProTα is reproduced in cerebral and retinal ischemia-reperfusion models. Further studies that used a retinal ischemia-reperfusion model revealed that ProTα protects retinal cells via ecto-F₁ ATPase coupled with the G_i-coupled P2Y₁₂ receptor and Toll-like receptor 4 (TLR4)/MD2 coupled with a Toll-IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF). In cerebral ischemia-reperfusion models, ProTα has additional survival mechanisms via an inhibition of matrix metalloproteases in microglia and vascular endothelial cells. Heterozygous or conditional ProTα knockout mice show phenotypes of anxiety, memory learning impairment, and a loss of neurogenesis. There are many reports that ProTα has multiple intracellular functions for cell survival and proliferation through a variety of protein-protein interactions. Overall, it is suggested that ProTα plays a key role as a brain guardian against ischemia stress through a cell-death-mode switch assisted by NTFs and a role of neurogenesis.

Isolation, Identification, and Characterization of Bioactive Peptides in Human Bone Cells from Tortoiseshell and Deer Antler Gelatin

Tortoiseshell and deer antler gelatin has been used to treat bone diseases in Chinese society. A pepsin-digested gelatin peptide with osteoblast-proliferation-stimulating properties was identified via LC-MS/MS. The resulting pentapeptide, TSKYR, was presumably subjected to further degradation into TSKY, TSK, and YR fragments in the small intestine. The above four peptides were chemically synthesized. Treatment of tripeptide TSK can lead to a significant 30- and 50-fold increase in the mineralized nodule area and density in osteoblast cells and a 47.5% increase in the number of chondrocyte cells. The calcium content in tortoiseshell was relatively higher than in human soft tissue. The synergistic effects of calcium ions and the peptides were observed for changes in osteoblast proliferation and differentiation. Moreover, these peptides can enhance the expression of RUNX2, OCN, FGFR2, and FRFR3 genes in osteoblasts, and aggrecan and collagen type II in chondrocyte (patent pending).

Review of Kyotorphin Research: A Mysterious Opioid Analgesic Dipeptide and Its Molecular, Physiological, and Pharmacological Characteristics

Tyrosine-arginine (kyotorphin), an opioid analgesic dipeptide, was discovered more than 40 years ago in 1979. The evidence accumulated during this period has established the physiological significance of kyotorphin as a neuromodulating peptide, and pharmacological applications. Some of the following important findings have been discussed in this review: (1) kyotorphin is unevenly distributed in the brain; it is found in high concentrations in the pain pathway, which involves the regions associated with morphine analgesia; (2) kyotorphin is subcellularly localized in the synaptosome fraction or nerve-ending particles; (3) a specific synthetase generates kyotorphin from tyrosine and arginine; (4) kyotorphin may be also processed from calpastatin by a novel calcium-activated neutral protease or calpain; (5) kyotorphin preloaded into the synaptosome is released by high K⁺ depolarization in a Ca²⁺-dependent manner; (6) kyotorphin has a specific G protein coupled receptor, which mediates the activation of phospholipase C (PLC) and inhibition of adenylyl cyclase through G_i; (7) leucine-arginine works as a specific kyotorphin receptor antagonist; 8) membrane-bound aminopeptidase or excretion through a peptide transporter, PEPT2, may contribute to the inactivation of kyotorphin; and (9) kyotorphin causes increased Met-enkephalin release from brain and spinal slices. It is also known that the opening of plasma membrane Ca²⁺ channels through a conformational coupling of the InsP₃ receptor with the transient receptor potential C1, which is downstream of the kyotorphin receptor-mediated activation of G_i and PLC, could be a potential underlying mechanism of Met-enkephalin release. Considering these findings, translational research is an exciting domain that can be explored in the future. As kyotorphin is a small molecule, we could design function-added kyotorphin derivatives. These studies would include not only the brain-permeable kyotorphin derivatives but also hybrid kyotorphin derivatives conjugated with small compounds that have additional pharmacological actions. Further, since there are reports of kyotorphin being involved in either the etiology or treatment of Alzheimer's disease, epilepsy, inflammation, and chronic pain, studies on the beneficial effects of kyotorphin derivatives should also be expected in the future.

Tyrosyl-tRNA synthetase: A potential kyotorphin synthetase in mammals

Kyotorphin (KTP; L-tyrosyl-l-arginine), an opioid-like analgesic discovered in the bovine brain, is potentially a neuromodulator because of its localization in synaptosomes, the existence of a specific KTP receptor, and the presence of its biosynthetic enzyme in the brain. KTP is formed in the brain from its constituent amino acids, L-tyrosine and L-arginine, by an enzyme termed KTP synthetase. However, the latter has never been identified. We aimed to test the hypothesis that tyrosyl-tRNA synthetase (TyrRS) is also KTP synthetase. We found that recombinant hTyrRS synthesizes KTP from tyrosine, arginine, and ATP, with Km = 1400 μM and 200 μM for arginine and tyrosine, respectively. TyrRS knockdown of PC12 cells with a small interfering RNA (siRNA) in the presence of 1.6 mM tyrosine, arginine, proline, or tryptophan significantly reduced the level of KTP, but not those of tyrosine-tyrosine, tyrosine-proline, or tyrosine-tryptophan. siRNA treatment did not affect cell survival or proliferation. In mice, TyrRS levels were found to be greater in the midbrain and medulla oblongata than in other brain regions. When arginine was administered 2 h prior to brain dissection, the KTP levels in these regions plus olfactory bulb significantly increased, although basal brain KTP levels remained relatively even. Our conclusion is further supported by a positive correlation across brain regions between TyrRS expression and arginine-accelerated KTP production.

cAMP and IP3 signaling pathways in HEK293 cells transfected with canine olfactory receptor genes

Olfactory receptors (ORs) expressed at the cell surface of olfactory sensory neurons lining the olfactory epithelium are the first actors of events leading to odor perception and recognition. As for other mammalian ORs, few dog OR have been deorphanized, mainly because of the absence of good methodology and the difficulties encountered to express ORs at the cell surface. Within this work, our aim was 1) to deorphanize a large subset of dog OR and 2) to compare the implication of the 2 main pathways, namely the cAMP and inositol 1,4,5-triphosphate (IP3) pathways, in the transduction of the olfactory message. For this, we used 2 independent tests to assess the importance of each of these 2 pathways and analyzed the responses of 47 canine family 6 ORs to a number of aliphatic compounds. We found these ORs globally capable of inducing intracellular calcium elevation through the IP3 pathway as confirmed by the use of specific inhibitors and/or a cAMP increase in response to aldehyde exposure. We showed that the implication of the cAMP or/and IP3 pathway was dependent upon the ligand-receptor combination rather than on one or the other partner. Finally, by exposing OR-expressing cells to the 21 possible pairs of C6-C12 aliphatic aldehydes, we confirmed that some odorant pairs may have an inhibitory or additive effect. Altogether, these results reinforce the notion that odorant receptor subfamilies may constitute functional units and call for a more systematic use of 2 complementary tests interrogating the cAMP and IP3 pathways when deorphanizing ORs.

Involvement of the long-chain fatty acid receptor GPR40 as a novel pain regulatory system

G-protein receptor (GPR) 40 is known to be activated by docosahexaenoic acid (DHA). However, reports studying the role and functions (including pain regulation) of GPR40 in the brain are lacking. We investigated the involvement of GPR40 in the brain on DHA-induced antinociceptive effects. Expression of GPR40 protein was observed in the olfactory bulb, striatum, hippocampus, midbrain, hypothalamus, medulla oblongata, cerebellum and cerebral cortex in the brain as well as the spinal cord, whereas GPR120 protein expression in these areas was not observed. Intracerebroventricular (i.c.v.), but not intrathecal (i.t.) injection of DHA (25 and 50μg/mouse) and GW9508 (a GPR40- and GPR120-selective agonist; 0.1 and 1.0μg/mouse) significantly reduced formalin-induced pain behavior. These effects were inhibited by pretreatment with the μ opioid receptor antagonist β-funaltrexamine (β-FNA), naltrindole (δ opioid receptor antagonist) and anti-β-endorphin antiserum. The κ opioid receptor antagonist norbinaltorphimine (nor-BNI) did not affect the antinociception of DHA or GW9508. Furthermore, the immunoreactivity of β-endorphin in the hypothalamus increased at 10 and 20min after i.c.v. injection of DHA and GW9508. These findings suggest that DHA-induced antinociception via β-endorphin release may be mediated (at least in part) through GPR40 signaling in the supraspinal area, and may provide valuable information on a novel therapeutic approach for pain control.

Ca(2+) channels on the move

The versatility of Ca(2+) as an intracellular messenger derives largely from the spatial organization of cytosolic Ca(2+) signals, most of which are generated by regulated openings of Ca(2+)-permeable channels. Most Ca(2+) channels are expressed in the plasma membrane (PM). Others, including the almost ubiquitous inositol 1,4,5-trisphosphate receptors (IP(3)R) and their relatives, the ryanodine receptors (RyR), are predominantly expressed in membranes of the sarcoplasmic or endoplasmic reticulum (ER). Targeting of these channels to appropriate destinations underpins their ability to generate spatially organized Ca(2+) signals. All Ca(2+) channels begin life in the cytosol, and the vast majority are then functionally assembled in the ER, where they may either remain or be dispatched to other membranes. Here, by means of selective examples, we review two issues related to this trafficking of Ca(2+) channels via the ER. How do cells avoid wayward activity of Ca(2+) channels in transit as they pass from the ER via other membranes to their final destination? How and why do some cells express small numbers of the archetypal intracellular Ca(2+) channels, IP(3)R and RyR, in the PM?

Plasma membrane IP3 receptors

IP3Rs (inositol 1,4,5-trisphosphate receptors) are expressed in the membranes of non-mitochondrial organelles in most animal cells, but their presence and role within the plasma membrane are unclear. Whole-cell patch-clamp recording from DT40 cells expressing native or mutated IP3Rs has established that each cell expresses just two or three functional IP3Rs in its plasma membrane. Only approx. 50% of the Ca2+ entry evoked by stimulation of the B-cell receptor is mediated by store-operated Ca2+ entry, the remainder appears to be carried by the IP3Rs expressed in the plasma membrane. Ca2+ entering the cell via just two large-conductance IP3Rs is likely to have very different functional consequences from the comparable amount of Ca2+ that enters through the several thousand low-conductance store-operated channels.

Odorant receptors directly activate phospholipase C/inositol-1,4,5-trisphosphate coupled to calcium influx in Odora cells

Mechanisms by which odorants activate signaling pathways in addition to cAMP are hard to evaluate in heterogeneous mixtures of primary olfactory neurons. We used single cell calcium imaging to analyze the response to odorant through odorant receptor (OR) U131 in the olfactory epithelial cell line Odora (Murrell and Hunter 1999), a model system with endogenous olfactory signaling pathways. Because adenylyl cyclase levels are low, agents activating cAMP formation do not elevate calcium, thus unmasking independent signaling mediated by OR via phospholipase C (PLC), inositol-1,4,5-trisphosphate (IP(3)), and its receptor. Unexpectedly, we found that extracellular calcium is required for odor-induced calcium elevation without the release of intracellular calcium, even though the latter pathway is intact and can be stimulated by ATP. Relevant signaling components of the PLC pathway and G protein isoforms are identified by western blot in Odora cells as well as in olfactory sensory neurons (OSNs), where they are localized to the ciliary zone or cell bodies and axons of OSNs by immunohistochemistry. Biotinylation studies establish that IP(3) receptors type 2 and 3 are at the cell surface in Odora cells. Thus, individual ORs are capable of elevating calcium through pathways not directly mediated by cAMP and this may provide another avenue for odorant signaling in the olfactory system.

Stimulation of peripheral nociceptor endings by low dose morphine and its signaling mechanism

In this report, we demonstrated that peripheral application of very low dose (amol ranges) of morphine induced flexor response through a substance P (SP) release at the nociceptor endings in mice. The intraplantar (i.pl.) application of morphine produced flexor response in a dose-dependent manner from 0.1 to 1000amol. The mu-opioid receptor (MOP-R) agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) also produced dose-dependent flexor response in same dose ranges. Morphine-induced flexor responses were markedly inhibited by naloxone and D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr amide (CTOP) both MOP-R antagonists and by intrathecal injection of antisense oligodeoxynucleotide (AS-ODN) for MOP-R which is expected to reduce the receptor expression in sensory nerve endings. Prior incubation with capsaicin, a depletor of SP from polymodal C fibers and [(+)-(2S,3S)-(2-methoxybenzylamino)-2-phenylpiperidine] (CP-99994), a tachykinin 1 receptor antagonist, also blocked the morphine-induced flexor responses. Moreover, pertussis toxin (PTX) which inactivates G(alpha)(i/o); [(1-[6-([(17b)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino)hexyl]-1H-pyrrole-2,5-dione)] (U-73122), an inhibitor of phospholipase C (PLC); ethyleneglycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA), a Ca(2+) chelating agent; xestospongin C, a membrane-permeable inositol trisphosphate (InsP(3)) receptor antagonist inhibited the morphine-flexor responses. However, thapsigargin, a depletor of intracellular Ca(2+) concentration and diphenhydramine, a histamine (His) H1 receptor antagonist, were unable to block the morphine-induced flexor responses. These results suggest that extremely low doses of morphine can stimulate sensory nerve endings through activation of peripheral MOP-R and its downstream mechanisms include activation of PLC through a SP release from polymodal C fibers.

Functional IP3- and ryanodine-sensitive calcium stores in presynaptic varicosities of NG108-15 (rodent neuroblastoma x glioma hybrid) cells

Presynaptic varicosities of the model neuronal cell line NG108-15, a cholinergic neuroblastoma cell x glioma cell hybrid capable of innervating striated myotubes, were examined for the presence of inositol 1,4,5-trisphosphate (IP3)-sensitive and Ca2+-activated (ryanodine-sensitive) Ca2+ stores using confocal microscopic imaging of Ca2+-sensitive fluorescent dye loaded into the cells. Initial demonstration of the presence of IP3 receptors and ryanodine receptors in the NG108-15 varicosities was obtained using immunocytochemistry. Treatment of NG108-15 cells with bradykinin (0.1 microM), whose receptor is linked to IP3 generation, and separately, caffeine (10 mM), an activator of endoplasmic reticulum ryanodine receptors, resulted in substantial increases in [Ca2+]i in the varicosities. K+-evoked changes in [Ca2+]i in the varicosities were reduced (52 %) after emptying the ryanodine-sensitive Ca2+ store using caffeine (10 mM), but were not affected by prior depletion of the IP3-sensitive Ca2+ store using thapsigargin (1 microM). Bradykinin-induced changes in [Ca2+]i were abolished following depletion of the IP3-sensitive Ca2+ store using thapsigargin (1 microM) and were reduced (72 %) by prior emptying of the ryanodine-sensitive Ca2+ store with caffeine (10 mM). The same results were obtained when the varicosities of the NG108-15 cells had formed synaptic junctions with co-cultured rat hindlimb myotubes. Taken together, the results suggest that, in the varicosities, activation of the IP3 pathway evoked the release of Ca2+ from the IP3-sensitive store, which, in turn, secondarily induced the release of Ca2+ from the ryanodine-sensitive store via Ca2+-induced Ca2+ release, and that depolarization-induced Ca2+ entry evoked Ca2+-induced Ca2+ release only from the ryanodine-sensitive store. Thus, functional internal Ca2+ stores are inherent components of presynaptic varicosities in this neural cell line.

Functional IP3- and ryanodine-sensitive calcium stores in presynaptic varicosities of NG108-15 (rodent neuroblastoma x glioma hybrid) cells

Presynaptic varicosities of the model neuronal cell line NG108-15, a cholinergic neuroblastoma cell x glioma cell hybrid capable of innervating striated myotubes, were examined for the presence of inositol 1,4,5-trisphosphate (IP3)-sensitive and Ca2+-activated (ryanodine-sensitive) Ca2+ stores using confocal microscopic imaging of Ca2+-sensitive fluorescent dye loaded into the cells. Initial demonstration of the presence of IP3 receptors and ryanodine receptors in the NG108-15 varicosities was obtained using immunocytochemistry. Treatment of NG108-15 cells with bradykinin (0.1 microM), whose receptor is linked to IP3 generation, and separately, caffeine (10 mM), an activator of endoplasmic reticulum ryanodine receptors, resulted in substantial increases in [Ca2+]i in the varicosities. K+-evoked changes in [Ca2+]i in the varicosities were reduced (52 %) after emptying the ryanodine-sensitive Ca2+ store using caffeine (10 mM), but were not affected by prior depletion of the IP3-sensitive Ca2+ store using thapsigargin (1 microM). Bradykinin-induced changes in [Ca2+]i were abolished following depletion of the IP3-sensitive Ca2+ store using thapsigargin (1 microM) and were reduced (72 %) by prior emptying of the ryanodine-sensitive Ca2+ store with caffeine (10 mM). The same results were obtained when the varicosities of the NG108-15 cells had formed synaptic junctions with co-cultured rat hindlimb myotubes. Taken together, the results suggest that, in the varicosities, activation of the IP3 pathway evoked the release of Ca2+ from the IP3-sensitive store, which, in turn, secondarily induced the release of Ca2+ from the ryanodine-sensitive store via Ca2+-induced Ca2+ release, and that depolarization-induced Ca2+ entry evoked Ca2+-induced Ca2+ release only from the ryanodine-sensitive store. Thus, functional internal Ca2+ stores are inherent components of presynaptic varicosities in this neural cell line.

Characterization of a phosphoinositide-mediated odor transduction pathway reveals plasma membrane localization of an inositol 1,4, 5-trisphosphate receptor in lobster olfactory receptor neurons

The role of phosphoinositide signaling in olfactory transduction is still being resolved. Compelling functional evidence for the transduction of odor signals via phosphoinositide pathways in olfactory transduction comes from invertebrate olfactory systems, in particular lobster olfactory receptor neurons. We now provide molecular evidence for two components of the phosphoinositide signaling pathway in lobster olfactory receptor neurons, a G protein alpha subunit of the G(q) family and an inositol 1,4, 5-trisphosphate-gated channel or an inositol 1,4,5-trisphosphate (IP(3)) receptor. Both proteins localize to the site of olfactory transduction, the outer dendrite of the olfactory receptor neurons. Furthermore, the IP(3) receptor localizes to membranes in the ciliary transduction compartment of these cells at both the light microscopic and electron microscopic levels. Given the absence of intracellular organelles in the sub-micron diameter olfactory cilia, this finding indicates that the IP(3) receptor is associated with the plasma membrane and provides the first definitive evidence for plasma membrane localization of an IP(3)R in neurons. The association of the IP(3) receptor with the plasma membrane may be a novel mechanism for regulating intracellular cations in restricted cellular compartments of neurons.

Ion channels in presynaptic nerve terminals and control of transmitter release

The primary function of the presynaptic nerve terminal is to release transmitter quanta and thus activate the postsynaptic target cell. In almost every step leading to the release of transmitter quanta, there is a substantial involvement of ion channels. In this review, the multitude of ion channels in the presynaptic terminal are surveyed. There are at least 12 different major categories of ion channels representing several tens of different ion channel types; the number of different ion channel molecules at presynaptic nerve terminals is many hundreds. We describe the different ion channel molecules at the surface membrane and inside the nerve terminal in the context of their possible role in the process of transmitter release. Frequently, a number of different ion channel molecules, with the same basic function, are present at the same nerve terminal. This is especially evident in the cases of calcium channels and potassium channels. This abundance of ion channels allows for a physiological and pharmacological fine tuning of the process of transmitter release and thus of synaptic transmission.

Low dose of kyotorphin (tyrosine-arginine) induces nociceptive responses through a substance P release from nociceptor endings

The intraplantar injection of kyotorphin (Kyo) elicited nociceptive flexor responses in mice in a dose-dependent manner between 0.1 and 100 fmol. These actions were completely blocked by substance P (NK1) receptor antagonists, such as CP-96345 and CP-99994, but not by their inactive derivatives, CP-96344 or CP-100263, nor by MEN-10376, an NK2 antagonist. Kyo-responses were also abolished by the local pretreatment with capsaicin to deplete substance P from nociceptor endings, and in tachykinin 1 gene K/O mice. These findings suggest that Kyo indirectly stimulates nociceptor endings through a local substance P release.

In vivo molecular signal transduction of peripheral mechanisms of pain

Although we have obtained a number of pharmacological tools and mutant mice lacking specific genes related to the pain, the distinct molecular basis of the pain-producing mechanism has remained to be fully clarified since we have been using conventional paradigms of the nociception test that may drive multiple endogenous molecules affecting nociception at the same time. Here, I will introduce a new paradigm of the nociception test. In this test, we focused on polymodal C-fibers by measuring nociceptive flexor responses induced by the peripheral application of a single species of nociceptive molecule. In addition, we identified the site of drug actions on nociceptor endings by the fact that the nociception was abolished by the intrathecal pretreatment with antisense oligodeoxynucleotide for receptors. Throughout experiments using this paradigm of the nociception test, it was firstly revealed that substance P, a major neurotransmitter of polymodal C-fibers, directly stimulates nociceptor endings through activation of Gq/11 and phospholipase C, followed by Ca2+ influx through plasma membrane-bound inositol trisphosphate receptors, and that bradykinin and histamine, both endogenous representative pain-producing substances, share this mechanism. Another unique mechanism is through Gi-coupled receptors such as receptors for nociceptin (orphanin FQ) or kyotorphin (tyrosine-arginine). The latter mechanism was found to be mediated through a substance P release from nociceptor endings. Future studies including some modifications of this paradigm should be also clinically useful for neuropathic pain research as well as understanding of pain physiology.

Characterization of inositol-1,4,5-trisphosphate-gated channels in the plasma membrane of rat olfactory neurons

It is generally accepted that inositol-1,4,5-trisphosphate (InsP3) plays a role in olfactory transduction. However, the precise mode of action of InsP3 remains controversial. We have characterized the conductances activated by the addition of 10 microM InsP3 to excised patches of soma plasma membrane from rat olfactory neurons. InsP3 induced current fluctuations in 25 of 121 inside-out patches. These conductances could be classified into two groups according to the polarity of the current at a holding potential of +40 to +60 mV (with Ringer's in the pipette and pseudointracellular solution in the bath). Conductances mediating outward currents could be further divided into large- (64 +/- 4 pS, n = 4) and small- (16 +/- 1.7 pS, n = 11) conductance channels. Both small- and large-conductance channels were nonspecific cation channels. The large-conductance channel displayed bursting behavior at +40 mV, with flickering increasing at negative holding potentials to the point where single-channel currents were no longer discernible. The small-conductance channel did not display flickering behavior. The conductance mediating inward currents at +40 to +60 mV reversed at +73 +/- 4 mV (n = 4). The current traces displayed considerable fluctuations, and single-channel currents could not be discerned. The current fluctuations returned to baseline after removal of InsP3. The power density spectrum for the excess noise generated by InsP3 followed a 1/f dependence consistent with conductance fluctuations in the channel mediating this current, although other mechanisms are not excluded. These experiments demonstrate the presence of plasma membrane InsP3-gated channels of different ionic specificity in olfactory receptor cells.

The role of inositol 1,4,5-trisphosphate 5-phosphatase in inositol signaling in the CNS of larval Manduca sexta

Production of inositol 1,4,5-trisphosphate (IP3) in cells results in the mobilization of intracellular calcium. Therefore, the dynamics of IP3 metabolism is important for calcium dependent processes in cells. This report investigates the coupling of mAChRs to the inositol lipid pathway in the CNS of the larval Manduca sexta. Stimulation of intact abdominal ganglia prelabeled with [3H]-inositol using a muscarinic agonist, oxotremorine-M (oxo-M), increased total inositol phosphate levels in a dose dependent manner (EC50 = 4.23 microM). These inositol phosphates consisted primarily of inositol 1,4-bisphosphate (IP2) and inositol monophosphate (IP1). Similarly, when nerve cord homogenates were provided with [3H]-phosphatidylinositol 4,5-bisphosphate ([3H]-PIP2) (10-13 microM) the predominant products were IP2 and IP1. In contrast, incubation of purified membranes with 1 mM oxo-M in the presence of 100 microM GTP gamma S and [3H]-PIP2 increased IP3 levels, suggesting that the direct activation of phospholipase C (PLC) by mAChRs occurs in a membrane delimited process. Together, these results suggest that in the intact nerve cord and in crude homogenates, a cytosolic 5-phosphatase quickly metabolizes IP3 to produce to IP2 and IP1. This enzyme was kinetically characterized using IP3 (Km = 43.7 microM, Vmax = 864 pmoles/min/mg) and IP4 (Km = 0.93 microM; Vmax = 300pmoles/min/mg) as substrates. The enzyme activity can be potently inhibited by two IP thiol compounds; IP3S3 (1,4,6) and IP3S3 (2,3,5), that show complex binding kinetics (Hill numbers < 1) and can distinguish different forms of the 5-phosphatase in purified membranes. These two inhibitors could be very useful tools to determine the role of the inositol lipid pathway in neuroexcitability.

Nociceptin/orphanin FQ-induced nociceptive responses through substance P release from peripheral nerve endings in mice

We have studied the in vivo signaling mechanisms involved in nociceptin/orphanin FQ (Noci)-induced pain responses by using a flexor-reflex paradigm. Noci was 10,000 times more potent than substance P (SP) in eliciting flexor responses after intraplantar injection into the hind limb of mice, but the action of Noci seems to be mediated by SP. Mice pretreated with an NK1 tachykinin receptor antagonist or capsaicin, or mice with a targeted disruption of the tachykinin 1 gene no longer respond to Noci. The action of Noci appears to be mediated by the Noci receptor, a pertussis toxin-sensitive G protein-coupled receptor that stimulates inositol trisphosphate receptor and Ca2+ influx. These findings suggest that Noci indirectly stimulates nerve endings of nociceptive primary afferent neurons through a local SP release.

The effect of neuropeptides kyotorphin and neokyotorphin on proliferation of cultured brown preadipocytes

Stimulation of DNA and protein synthesis in brown preadipocytes by 1 microM neokyotorphin in serum-containing media was comparable with the effect of 1 microM norepinephrine. In serum-free medium a decrease and a shift of the maximal effect to lower concentration of neokyotorphin were observed. Kyotorphin had no effect on cell proliferation in either medium; however, 0.01-1 microM kyotorphin inhibited the cell proliferation stimulated by 1 microM norepinephrine. Norepinephrine and both peptides stimulated comparable Ca2+ rise in freshly isolated brown preadipocytes. The effects of neokyotorphin and norepinephrine were additive, whereas 0.03-0.3 microM kyotorphin blocked the action of 3 microM norepinephrine. The peptides did not affect the cAMP level in non-stimulated or norepinephrine-stimulated cultured cells. The effects of the peptides on the brown fat cell cultures indicate that peripheral tissue cells contain receptors for these neuropeptides.