ryanodine and 1-amino-1-3-dicarboxycyclopentane

Rapid estrogen effects became an interesting topic to explain estrogen effects not associated with the classical nuclear pathway. The rapid estrogen effect on intracellular calcium oscillations was characterized in neurons of the arcuate nucleus. Ratiometric calcium imaging (fura-2AM) was used to measure intracellular calcium in brain slices of female Swiss Webster mice (median of age 27 days p.n.). Calcium oscillations were dependent on intracellular calcium and also on calcium influx from the extracellular space. The perfusion of slices with calcium-free solution inhibited spontaneous calcium oscillations. The metabotropic glutamate receptor agonist t-ACPD (5 microM) and low concentrated ryanodine (100 nM) induced intracellular calcium release when slices were perfused with calcium-free solution. 17beta-estradiol (10 nM) also induced intracellular calcium release in calcium-free ACSF. This effect was inhibited by the preceding administration of thapsigargin (2 microM) indicating the association of the rapid estrogen effect with intracellular calcium stores. The administration of the non-selective phospholipase C-inhibitor ET-18 (30 microM), but not U73122 (10 microM), and the inhibition of protein kinase A by H-89 (0.25 microM) suppressed the rapid estrogen effect. Analyses indicated a qualitative, but not quantitatively significant effect of 17beta-estradiol on calcium oscillations.

Topics: Animals; Arcuate Nucleus of Hypothalamus; Calcium; Calcium Channels; Calcium Signaling; Cyclic AMP-Dependent Protein Kinases; Cycloleucine; Estrogens; Female; Fura-2; In Vitro Techniques; Mice; Neurons; Receptors, Metabotropic Glutamate; Ryanodine; Sarcoplasmic Reticulum; Type C Phospholipases

Calcium waves in layer 2/3 and layer 5 neocortical somatosensory pyramidal neurons were examined in slices from 2- to 8-week-old rats. Repetitive synaptic stimulation evoked a delayed, all-or-none [Ca2+]i increase primarily on the main dendritic shaft. This component was blocked by 1 mM (R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG), 10 microM ryanodine, 1 mg ml-1 internal heparin, and was not blocked by 400 microM internal Ruthenium Red, indicating that it was due to Ca2+ release from internal stores by inositol 1,4,5-trisphosphate (IP3) mobilized via activation of metabotropic glutamate receptors. Calcium waves were initiated on the apical shaft at sites between the soma to around the main branch point, mostly at insertion points of oblique dendrites, and spread in both directions along the shaft. In the proximal dendrites the peak amplitude of the resulting [Ca2+]i change was much larger than that evoked by a train of Na+ spikes. In distal dendrites the peak amplitude was comparable to the [Ca2+]i change due to a Ca2+ spike. IP3-mediated Ca2+ release also was observed in the presence of the metabotropic agonists t-ACPD and carbachol when backpropagating spikes were generated. Ca2+ entry through NMDA receptors was observed primarily on the oblique dendrites. The main differences between waves in neocortical neurons and in previously described hippocampal pyramidal neurons were, (a) Ca2+ waves in L5 neurons could be evoked further out along the main shaft, (b) Ca2+ waves extended slightly further out into the oblique dendrites and (c) higher concentrations of bath-applied t-ACPD and carbachol were required to generate Ca2+ release events by backpropagating action potentials.

Topics: Action Potentials; Animals; Calcium; Carbachol; Cholinergic Agonists; Cycloleucine; Dendrites; Glycine; Heparin; In Vitro Techniques; Intracellular Membranes; Neocortex; Osmolar Concentration; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Ryanodine; Synapses; Tissue Distribution

The ability of metabotropic glutamate receptor activation to mobilise intracellular calcium was investigated in cultured dorsal root ganglion (DRG) neurones from neonatal rats using the calcium sensitive fluorescent dye Fura-2. L-glutamate (10 microM) caused sustained and oscillatory increases in intracellular calcium concentration ([Ca2+]i) in a subpopulation of cultured DRG neurones. The oscillatory responses were not blocked by combined application of the ionotropic glutamate receptor antagonists MK 801 (2 microM) and CNQX (20 microM). Oscillations in [Ca2+]i were also observed following application of the nonselective metabotropic glutamate receptor (mGluR) agonist, trans-(1S,3R)-1-aminocyclopentane-1S, 3R-dicarboxylic acid (1S,3R)-ACPD, 20 microM) and the mGluR5 agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG, 500 microM). These responses were blocked by the selective Group I mGluR antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) (100 microM) and Ca2+ release channel inhibitors ryanodine (100 microM) and dantrolene (10 microM). The predominantly Group II agonist (2S,2'R,3'R)-2-(2'3'-dicarboxy-cyclopropyl)glycine (DCG-IV, 100 microM) failed to produce Ca2+ transients alone but suppressed responses to CHPG. Reverse transcriptase PCR techniques, using primers specific to Group I mGluRs, revealed the presence of mGluR5 but not mGluR1 mRNA in these cells. Therefore, glutamate can cause a slowly activating and reversible mobilisation of [Ca2+]i in sensory neurones by activation of ionotropic receptors, and can induce oscillatory calcium transients by selectively activating metabotropic glutamate receptors that are likely to be of the mGluR5 subtype.

Topics: Animals; Animals, Newborn; Calcium; Calcium Channel Blockers; Cells, Cultured; Cycloleucine; Cyclopropanes; Dantrolene; Fluorescence; Ganglia, Spinal; Glutamic Acid; Glycine; Indans; Phenylacetates; Rats; Rats, Sprague-Dawley; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Ryanodine; Ryanodine Receptor Calcium Release Channel; Stereoisomerism

Neurons of the avian cochlear nucleus, nucleus magnocellularis (NM), are activated by glutamate released from auditory nerve terminals. If this stimulation is removed, the intracellular calcium ion concentration ([Ca2+]i) of NM neurons rises and rapid atrophic changes ensue. We have been investigating mechanisms that regulate [Ca2+]i in these neurons based on the hypothesis that loss of Ca2+ homeostasis causes the cascade of cellular changes that results in neuronal atrophy and death. In the present study, video-enhanced fluorometry was used to monitor changes in [Ca2+]i stimulated by agents that mobilize Ca2+ from intracellular stores and to study the modulation of these responses by glutamate. Homobromoibotenic acid (HBI) was used to stimulate inositol trisphosphate (IP3)-sensitive stores, and caffeine was used to mobilize Ca2+ from Ca2+-induced Ca2+ release (CICR) stores. We provide data indicating that Ca2+ responses attributable to IP3- and CICR-sensitive stores are inhibited by glutamate, acting via a metabotropic glutamate receptor (mGluR). We also show that activation of C-kinase by a phorbol ester will reduce HBI-stimulated calcium responses. Although the protein kinase A accumulator, Sp-cAMPs, did not have an effect on HBI-induced responses. CICR-stimulated responses were not consistently attenuated by either the phorbol ester or the Sp-cAMPs. We have previously shown that glutamate attenuates voltage-dependent changes in [Ca2+]i. Coupled with the present findings, this suggests that in these neurons mGluRs serve to limit fluctuations in intracellular Ca2+ rather than increase [Ca2+]i. This system may play a role in protecting highly active neurons from calcium toxicity resulting in apoptosis.

Topics: Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Alanine; Animals; Benzoates; Caffeine; Calcium; Calcium Channel Blockers; Calcium Channels; Calcium Signaling; Chelating Agents; Chick Embryo; Cochlear Nucleus; Cyclic AMP; Cycloleucine; Cysteine; Egtazic Acid; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Fluorescent Dyes; Fura-2; Gallic Acid; Glutamic Acid; Glycine; Ibotenic Acid; Inositol 1,4,5-Trisphosphate Receptors; Ion Channel Gating; Neurons; Neuroprotective Agents; Neurotransmitter Agents; Patch-Clamp Techniques; Phosphodiesterase Inhibitors; Receptors, Cytoplasmic and Nuclear; Ryanodine; Second Messenger Systems; Thionucleotides

Presynaptic metabotropic glutamate receptors (mGluRs) modulate the release of transmitter from most central synapses. However, difficulties in recording from presynaptic structures has lead to an incomplete understanding of the mechanisms underlying these fundamental processes. By recording directly from presynaptic reticulospinal axons and postsynaptic motoneurons of the lamprey spinal cord, we have obtained electrophysiological and optical evidence that vertebrate presynaptic metabotropic glutamate receptors modulate neurotransmitter release at this synapse through two distinct mechanisms: (1) mGluR activation in the presynaptic terminal depresses transmitter release by activating a presynaptic K+ current, and (2) mGluR activation enhances transmitter release by amplifying the action potential-evoked presynaptic Ca2+ signal by rapidly releasing Ca2+ from intracellular stores in a Ca2+-dependent manner. Furthermore, this effect is mediated by physiological release of glutamate from the presynaptic terminals. These autoreceptor-mediated processes are likely to generate complex effects on transmitter release evoked by repetitive stimulation.

Topics: 4-Aminopyridine; Animals; Calcium; Cycloleucine; Electrophysiology; Excitatory Amino Acid Antagonists; Glycine; Lampreys; Membrane Potentials; Motor Neurons; Neuroprotective Agents; Neurotransmitter Agents; Potassium; Presynaptic Terminals; Receptors, Metabotropic Glutamate; Resorcinols; Ryanodine; Spinal Cord; Synaptic Transmission

In skeletal muscle, L-type Ca2+ channels act as voltage sensors to control ryanodine-sensitive Ca2+ channels in the sarcoplasmic reticulum. It has recently been demonstrated that these ryanodine receptors generate a retrograde signal that modifies L-type Ca2+ -channel activity. Here we demonstrate a tight functional coupling between ryanodine receptors and L-type Ca2+ channel in neurons. In cerebellar granule cells, activation of the type-1 metabotropic glutamate receptor (mGluR1) induced a large, oscillating increase of the L-type Ba2+ current. Activation occurred independently of inositol 1,4,5-trisphosphate and classical protein kinases, but was mimicked by caffeine and blocked by ryanodine. The kinetics of this blockade were dependent on the frequency of Ba2+ current stimulation. Both mGluR1 and caffeine-induced increase in L-type Ca2+ -channel activity persisted in inside-out membrane patches. In these excised patches, ryanodine suppressed both the mGluR1- and caffeine-activated L-type Ca2+ channels. These results demonstrate a novel mechanism for Ca2+ -channel modulation in neurons.

Topics: Animals; Barium; Caffeine; Calcium Channels; Cells, Cultured; Cerebellum; Cycloleucine; Inositol 1,4,5-Trisphosphate; Membrane Potentials; Mice; Muscle Proteins; Neurons; Phosphodiesterase Inhibitors; Protein Kinases; Receptors, Metabotropic Glutamate; Ryanodine; Ryanodine Receptor Calcium Release Channel; Type C Phospholipases

1. The single-electrode voltage-clamp technique was used to study the effects of the metabotropic glutamate receptors (mGluRs) agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD, ACPD, 3-10 microM) on CA3 hippocampal neurons during the 1st 10 days of postnatal (P) life and in adulthood. 2. Repeated applications of 1S,3R-ACPD, in the presence of tetrodotoxin (TTX, 1 microM), tetraethylammonium chloride (TEACl 10 mM), and CsCl (2 mM), induced in immature but not in adult neurons periodic inward currents (PICs) that persisted for several hours after the last application of the agonist. 3. PICs, which were generated by nonspecific cationic currents, reversed polarity at 2.8 +/- 3 (SD) mV. They were reversibly blocked by kynurenic acid (1 mM), suggesting that they were mediated by glutamate acting on ionotropic receptors. They were also abolished in a nominally Ca(2+)-free medium. 4. PICs were irreversibly abolished by thapsigargin (10 microM) but were unaffected by ryanodine (10-40 microM). Caffeine (2 mM) also reversibly blocked PICs; this effect was independent from adenosine 3',5'-cyclic monophosphate (cAMP) accumulation, inhibition of voltage-dependent Ca2+ current, or blockade of adenosine receptors. 5. We suggest that, in neonatal slices, mGluRs-induced PICs are triggered by elevation of [Ca2+]i, after mobilization of Ca2+ from inositol 1,4,5-trisphosphate (InsP3)-sensitive stores. This will lead to a persistent, pulsatile release of glutamate from presynaptic nerve terminals, a phenomenon that is probably maintained via a calcium-induced-calcium release process.

Topics: Animals; Animals, Newborn; Caffeine; Calcium; Cycloleucine; Electrophysiology; Hippocampus; In Vitro Techniques; Inositol 1,4,5-Trisphosphate; Neurons; Neurotoxins; Patch-Clamp Techniques; Potassium Channels; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Ryanodine; Sodium Channels; Tetrodotoxin