thapsigargin and 1-amino-1-3-dicarboxycyclopentane

1. The metabotropic glutamate receptor (mGluR) agonist trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (trans-ACPD) (10-100 microM) depolarized isolated frog spinal cord motoneurones, a process sensitive to kynurenate (1.0 mM) and tetrodotoxin (TTX) (0.783 microM). 2. In the presence of NMDA open channel blockers [Mg2+; (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK801); 3,5-dimethyl-1-adamantanamine hydrochloride (memantine)] and TTX, trans-ACPD significantly potentiated NMDA-induced motoneurone depolarizations, but not alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA)- or kainate-induced depolarizations. 3. NMDA potentiation was blocked by (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) (240 microM), but not by alpha-methyl-(2S,3S,4S)-alpha-(carboxycyclopropyl)-glycine (MCCG) (290 microM) or by alpha-methyl-(S)-2-amino-4-phosphonobutyrate (L-MAP4) (250 microM), and was mimicked by 3,5-dihydroxyphenylglycine (DHPG) (30 microM), but not by L(+)-2-amino-4-phosphonobutyrate (L-AP4) (100 microM). Therefore, trans-ACPD's facilitatory effects appear to involve group I mGluRs. 4. Potentiation was prevented by the G-protein decoupling agent pertussis toxin (3-6 ng ml(-1), 36 h preincubation). The protein kinase C inhibitors staurosporine (2.0 microM) and N-(2-aminoethyl)-5-isoquinolinesulphonamide HCI (H9) (77 microM) did not significantly reduce enhanced NMDA responses. Protein kinase C activation with phorbol-12-myristate 13-acetate (5.0 microM) had no effect. 5. Intracellular Ca2+ depletion with thapsigargin (0.1 microM) (which inhibits Ca2+/ATPase), 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetracetic acid acetyl methyl ester (BAPTA-AM) (50 microM) (which buffers elevations of [Ca2+]i), and bathing spinal cords in nominally Ca2+-free medium all reduced trans-ACPD's effects. 6. The calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W7) (100 microM) and chlorpromazine (100 microM) diminished the potentiation. 7. In summary, group I mGluRs selectively facilitate NMDA-depolarization of frog motoneurones via a G-protein, a rise in [Ca2+]i from the presumed generation of phosphoinositides, binding of Ca2+ to calmodulin, and lessening of the Mg2+-produced channel block of the NMDA receptor.

Topics: Amino Acids, Dicarboxylic; Aminobutyrates; Animals; Benzoates; Calcium; Calcium-Calmodulin-Dependent Protein Kinases; Chlorpromazine; Cycloleucine; Dose-Response Relationship, Drug; Drug Synergism; Egtazic Acid; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glycine; GTP-Binding Proteins; In Vitro Techniques; Kynurenic Acid; Magnesium; Membrane Potentials; Motor Neurons; N-Methylaspartate; Neuroprotective Agents; Pertussis Toxin; Rana pipiens; Receptors, Metabotropic Glutamate; Reflex; Resorcinols; Second Messenger Systems; Spinal Cord; Sulfonamides; Tetrodotoxin; Thapsigargin; Virulence Factors, Bordetella

Metabotropic glutamate receptors modulate neuronal excitability via a multitude of mechanisms, and they have been implicated in the pathogenesis of neurodegenerative processes. Here we investigated the responses mediated by group I metabotropic glutamate receptors (mGluRs) in dopamine neurons of the rat substantia nigra pars compacta, using whole cell patch-clamp recordings in combination with microfluorometric measurements of [Ca(2+)](i) and [Na(+)](i). The selective group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (3,5-DHPG) was bath-applied (20 microM, 30 s to 2 min) or applied locally by means of short-lasting (2-4 s) pressure pulses, delivered through an agonist-containing pipette positioned close to the cell body of the neuron. 3,5-DHPG evoked an inward current characterized by a transient and a sustained component, the latter of which was uncovered only with long-lasting agonist applications. The fast component coincided with a transient elevation of [Ca(2+)](i), whereas the total current was associated with a rise in [Na(+)](i). These responses were not affected either by the superfusion of ionotropic excitatory amino acid antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and D-2-amino-5-phosphono-pentanoic acid (D-APV), nor by the sodium channel blocker tetrodotoxin (TTX). (S)-alpha-methyl-4-carboxyphenylglycine (S-MCPG) and the more selective mGluR1 antagonist 7(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate (CPCCOEt) depressed both 3,5-DHPG-induced inward current components and, although less effectively, the associated [Ca(2+)](i) elevations. On repeated agonist applications the inward current and the calcium transients both desensitized. The time constant of recovery from desensitization differed significantly between these two responses, being 67.4+/-4.4 s for the inward current and 28.6+/-2.7 s for the calcium response. Bathing the tissue in a calcium-free/EGTA medium or adding thapsigargin (1 microM) to the extracellular medium prevented the generation of the [Ca(2+)](i) transient, but did not prevent the activation of the inward current. These electrophysiological and fluorometric results show that the 3, 5-DHPG-induced inward current and the [Ca(2+)](i) elevations are mediated by independent pathways downstream the activation of mGluR1.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Calcium; Chromones; Cycloleucine; Egtazic Acid; Excitatory Amino Acid Antagonists; Glycine; In Vitro Techniques; Microscopy, Fluorescence; Neurons; Patch-Clamp Techniques; Rats; Receptors, Metabotropic Glutamate; Resorcinols; Substantia Nigra; Tetrodotoxin; Thapsigargin

Calcium influx and elevation of intracellular free calcium ([Ca2+]i), with subsequent activation of degradative enzymes, is hypothesized to cause cell injury and death after traumatic brain injury. We examined the effects of mild-to-severe stretch-induced traumatic injury on [Ca2+]i dynamics in cortical neurons cultured on silastic membranes. [Ca2+]i was rapidly elevated after injury, however, the increase was transient with neuronal [Ca2+]i returning to basal levels by 3 h after injury, except in the most severely injured cells. Despite a return of [Ca2+]i to basal levels, there were persistent alterations in calcium-mediated signal transduction through 24 h after injury. [Ca2+]i elevation in response to glutamate or NMDA was enhanced after injury. We also found novel alterations in intracellular calcium store-mediated signaling. Neuronal calcium stores failed to respond to a stimulus 15 min after injury and exhibited potentiated responses to stimuli at 3 and 24 h post-injury. Thus, changes in calcium-mediated cellular signaling may contribute to the pathology that is observed after traumatic brain injury.

Topics: Animals; Brain Injuries; Calcium; Calcium Signaling; Cells, Cultured; Cerebral Cortex; Cycloleucine; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Glutamic Acid; N-Methylaspartate; Neuroglia; Neurons; Neuroprotective Agents; Rats; Rats, Sprague-Dawley; Thapsigargin

We have previously developed an in vitro model for traumatic brain injury that simulates a major component of in vivo trauma, that being tissue strain or stretch. We have validated our model by demonstrating that it produces many of the posttraumatic responses observed in vivo. Sustained elevation of the intracellular free calcium concentration ([Ca2+]i) has been hypothesized to be a primary biochemical mechanism inducing cell dysfunction after trauma. In the present report, we have examined this hypothesis in astrocytes using our in vitro injury model and fura-2 microphotometry. Our results indicate that astrocyte [Ca2+]i is rapidly elevated after stretch injury, the magnitude of which is proportional to the degree of injury. However, the injury-induced [Ca2+]i elevation is not sustained and returns to near-basal levels by 15 min postinjury and to basal levels between 3 and 24 h after injury. Although basal [Ca2+]i returns to normal after injury, we have identified persistent injury-induced alterations in calcium-mediated signal transduction pathways. We report here, for the first time, that traumatic stretch injury causes release of calcium from inositol trisphosphate-sensitive intracellular calcium stores and may uncouple the stores from participation in metabotropic glutamate receptor-mediated signal transduction events. We found that for a prolonged period after trauma astrocytes no longer respond to thapsigargin, glutamate, or the inositol trisphosphate-linked metabotropic glutamate receptor agonist trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid with an elevation in [Ca2+]i. We hypothesize that changes in calcium-mediated signaling pathways, rather than an absolute elevation in [Ca2+]i, is responsible for some of the pathological consequences of traumatic brain injury.

Topics: Animals; Animals, Newborn; Astrocytes; Calcium; Cells, Cultured; Cerebral Cortex; Cycloleucine; Excitatory Amino Acid Agonists; Glutamic Acid; Inositol Phosphates; Intracellular Fluid; Rats; Rats, Sprague-Dawley; Stress, Mechanical; Thapsigargin

1. Spontaneous inhibitory postsynaptic currents (IPSCs) and evoked IPSCs were recorded by a whole-cell patch-recording technique from cultured Purkinje cells of the rat. The size of spontaneous IPSCs, after a train of depolarizing pulses was applied to the Purkinje cells, increased to 163 +/- 6% (mean +/- S.E.M., n = 7 cells) of the control levels measured before the stimulus train. 2. The GABAergic postsynaptic currents were recorded under voltage clamp from the synapse formed between two Purkinje cells. These IPSCs increased to 218 +/- 31% (n = 4) of control levels after depolarizing stimulation was applied to the postsynaptic Purkinje cells. Size-increased IPSCs were observed as long as recording continued and the phenomena will be called potentiation in this paper. 3. Intracellular application of Ruthenium Red (20 microM) did not block the potentiation of spontaneous IPSCs induced by the depolarizing stimulus (165 +/- 9%, n =6), but heparin (2 mg ml-1) partially blocked the potentiation (123 +/- 10%, n = 6). Heparin applied together with Ruthenium Red (20 microM) blocked potentiation completely (96 +/- 5%, n = 8) at concentrations higher than 1 mg ml-1. 4. Intracellular free calcium concentrations ([Ca2+]i) was monitored as the ratio of fura-2 fluorescences excited at 340 and 380 nm. In control cells, [Ca2+]i was increased by each depolarizing pulse. When Purkinje cells were dialysed with heparin or heparin with Ruthenium Red, the rise in [Ca2+]i was suppressed. 5. Bath application of thapsigargin (1 microM) blocked the potentiation (99 +/- 2%, n = 4) and suppressed the rise in [Ca2+]i. 6. When 30 mM BAPTA was applied intracellularly, a train of depolarizing pulses failed to induce potentiation of IPSCs and failed to raise [Ca2+]i. The results from points 3-6 suggest that the increase in [Ca2+]i, most probably coupled with the release from intracellular stores especially from the inositol trisphosphate (IP3)-sensitive stores, is crucial for the potentiation of IPSCs. 7. Bath application of a metabotropic glutamate receptor activator (t-ACPD, 200 microM) increased both the amplitude and frequency of spontaneous IPSCs and increased the [Ca2+]i slightly in dendrites. The inward current induced by the puff-applied GABA (2 microM) was increased, after t-ACPD application, to 186 +/- 36% of the control level (n = 3). Bath application of quisqualate (2 microM) caused a rapid increase in [Ca2+]i in dendrites and in the cell body and increased both the amplitud

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Calcium; Calcium Channels; Chelating Agents; Cycloleucine; Egtazic Acid; Enzyme Inhibitors; Estrenes; Evoked Potentials; Excitatory Amino Acid Antagonists; gamma-Aminobutyric Acid; Heparin; Neuroprotective Agents; Phosphodiesterase Inhibitors; Purkinje Cells; Pyrrolidinones; Rats; Receptors, Metabotropic Glutamate; Ruthenium Red; Synapses; Thapsigargin; Type C Phospholipases

Metabotropic glutamate receptors (mGluRs) in the CNS are coupled to a variety of second messenger systems, the best characterized of which is activation of phosphoinositide hydrolysis. Recently, we found that activation of mGluRs in rat brain slices by the selective mGluR agonist 1-aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD) potentiates cyclic AMP (cAMP) responses elicited by activation of other receptors coupled to Gs. It has been suggested that mGluR-mediated potentiation of cAMP responses is secondary to activation of phosphoinositide hydrolysis. However, preliminary evidence suggests that this is not the case. Therefore, we designed a series of experiments to test more fully the hypothesis that mGluR-mediated potentiation of cAMP responses is secondary to phosphoinositide hydrolysis. Inhibitors of both protein kinase C and intracellular calcium mobilization failed to antagonize 1S,3R-ACPD-stimulated potentiation of cAMP responses. Further, coapplication of phorbol esters and 1S,3R-ACPD induced a cAMP response that was greater than additive. Finally, (RS)-3,5-dihydroxyphenylglycine, a selective agonist of mGluRs coupled to phosphoinositide hydrolysis, failed to potentiate cAMP responses, whereas (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine, an mGluR agonist that does not activate mGluRs coupled to phosphoinositide hydrolysis, elicited a robust potentiation of cAMP responses. In total, these data strongly suggest that mGluR-mediated potentiation of cAMP responses is not secondary to activation of phosphoinositide hydrolysis and is likely mediated by a group II mGluR.

Topics: Animals; Brain; Calcium; Calcium-Transporting ATPases; Cyclic AMP; Cycloleucine; Glycine; Hydrolysis; In Vitro Techniques; Intracellular Membranes; Neurotoxins; Phosphatidylinositols; Protein Kinase C; Rats; Receptors, Metabotropic Glutamate; Resorcinols; Terpenes; Thapsigargin

We examined the effects of different types of glutamate receptor agonists on the intracellular calcium concentration, ([Ca2+]i), in cultured rat cortical glial cells. The cells in these cultures were characterized immunocytochemically using antibodies against glial fibrillary acidic protein, A2B5, and OX-42. The metabotropic glutamate receptor agonist (1S,3R)-1-aminocyclopentane-1,3- dicarboxylic acid produced Ca2+ mobilization from intracellular stores in all classes of cells. Agonists at non-NMDA glutamate receptors also produced large increases in [Ca2+]i, primarily in cells of the O-2A lineage. Disruption of intracellular Ca2+ stores with thapsigargin showed that increases in [Ca2+]i produced by activating AMPA/kainate receptors were primarily due to Ca2+ influx rather than Ca(2+)-induced Ca2+ release. Agonists at NMDA receptors were ineffective. Electrophysiological studies revealed that cells of the O-2A lineage exhibited moderate inward currents in response to kainate in Na(+)-containing solutions, but only small inward currents and outward rectification in Na(+)-free solutions. However, in the presence of cyclothiazide, the kainate-induced currents were increased in size and a rightward shift of the reversal potential with increased [Ca2+]o could be demonstrated. Activation of cells by kainate, but not by depolarizing stimuli, stimulated the uptake of Co2+. Polymerase chain reaction studies showed that the glutamate receptor subunits GluR1-4 and GluR6 were all expressed in these cultures, but GluR5 was absent. The nature of the Ca2+ uptake pathway activated by non-NMDA receptor agonists in the O-2A lineage population is discussed. It is considered most likely that the O-2A lineage cells express both non-NMDA receptors that are relatively impermeable to divalent cations, as well as a smaller population that are Ca2+ permeable.

Topics: Animals; Animals, Newborn; Base Sequence; Calcium; Calcium-Transporting ATPases; Cells, Cultured; Cerebral Cortex; Cycloleucine; DNA Primers; Fura-2; Ganglia, Spinal; Glial Fibrillary Acidic Protein; Immunohistochemistry; Kainic Acid; Kinetics; Macromolecular Substances; Membrane Potentials; Molecular Sequence Data; Neuroglia; Neurotoxins; Polymerase Chain Reaction; Rats; Receptors, Glutamate; Terpenes; Thapsigargin

The transient activation of the N-methyl-D-aspartate (NMDA) receptor system by high frequency (tetanic) stimulation results in a rapidly developing and long-lasting potentiation of synaptic transmission in the CA1 region of the hippocampus. This potentiation can be divided into an early decremental component, known as short-term potentiation (STP), and a more slowly developing persistent phase, termed long-term potentiation (LTP). Here we describe how activation of metabotropic glutamate receptors (mGluRs), by aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD), can induce the same stable form of LTP, but without the STP component. 1S,3R-ACPD-induced LTP does not require electrical stimulation during its induction, but is dependent on an intact connection between the CA3 and CA1 regions of the hippocampus. 1S,3R-ACPD-induced LTP circumvents the need for the activation of NMDA receptors and is likely to involve both the stimulation of protein kinase C (PKC) and the release of Ca2+ from intracellular stores.

Topics: Alkaloids; Animals; Calcium-Transporting ATPases; Cycloleucine; Electric Stimulation; Hippocampus; In Vitro Techniques; Neuronal Plasticity; Phosphatidylinositols; Protein Kinase C; Rats; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Signal Transduction; Staurosporine; Stereoisomerism; Synapses; Terpenes; Thapsigargin