Heteroceras gracile sp. nov., une espèce nouvelle d'Heteroceras Orbigny, 1849, du Barrémien supérieur de Morteiron (Alpes de Haute-Provence, France)

The species Heteroceras gracile sp. nov. is described; it is a small and slender species, with a small helix and hamuliniform morphology, previously considered as an atypical variant of Heteroceras baylei (Reynès, 1876). In southeast France, it is mainly known in the Morteiron section (Alpes de Haute-Provence, France), but the species is also present in Bulgaria and possibly in Japan.L'espèce Heteroceras gracile sp. nov. est créée ; elle est représentée par des formes de petite taille, à enroulement frêle et petit turricône, de morphologie hamuliniforme, précédemment considérées comme des morphes atypiques d'Heteroceras baylei (Reynès, 1876). Dans le sud-est de la France, elle est essentiellement connue dans la coupe de Morteiron (Alpes de Haute-Provence, France), mais l'espèce est aussi présente en Bulgarie et hypothétiquement au Japon

Relaxation and Stripping: The Evolution of Sizes, Dispersions and Dark Matter Fractions in Major and Minor Mergers of Elliptical Galaxies

We revisit collisionless major and minor mergers of spheroidal galaxies in the context of the size evolution of elliptical galaxies. The simulations are performed as a series of mergers with mass-ratios of 1:1 and 1:10 for models representing pure bulges as well as bulges embedded in dark matter halos. For major and minor mergers, respectively, we identify and analyze two different processes, violent relaxation and stripping, leading to size evolution and a change of the dark matter fraction within the observable effective radius. Violent relaxation - which is the dominant mixing process for major mergers but less important for minor mergers - scatters relatively more dark matter particles than bulge particles to small. Stripping in minor mergers assembles stellar satellite particles at large radii in halo dominated regions of the massive host. This strongly increases the size of the bulge into regions with higher dark matter fractions leaving the inner host structure almost unchanged. A factor of two mass increase by minor mergers increases the dark matter fraction by 20 per cent. We present analytic corrections to simple one-component virial estimates for the evolution of the gravitational radii. If such a two-component system grows by minor mergers alone its size growth, $r_{\mathrm{e}} \propto M^\alpha$, reaches values of $\alpha \approx 2.4$, significantly exceeding the simple theoretical limit of $\alpha = 2$. For major mergers the sizes grow with $\alpha \lesssim 1$. Our results indicate that minor mergers of galaxies embedded in massive dark matter halos provide a potential mechanism for explaining the rapid size growth and the build-up of massive elliptical systems predicting significant dark matter fractions and radially biased velocity dispersions at large radii (abbreviated)Comment: accepted for publication in MNRA

Specific Angular Momentum of Disc Merger Remnants and the λR\lambda_R-Parameter

We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the $\lambda_R$-parameter, which is a luminosity weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early type galaxies in so called fast $\lambda_R > 0.1$ and slow rotators $\lambda_R < 0.1$. Tests on merger remnants reveal that $\lambda_R$ is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of $\lambda_R$ values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in creating a slow or a fast rotator in a single binary merger, the former being created mostly in an equal mass merger. Slow rotators have a $\lambda_R$ which does not vary with projection. The confusion rate with face-on fast rotators is very small. Merger with low gas fractions form slow rotators with smaller ellipticities and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of $\lambda_R$ as high as our progenitor disc galaxies.Comment: 12 pages, 11Figures, submitted to MNRA

The influence of gas on the structure of merger remnants

We present a large set of merger simulations of early-type disc galaxies with mass ratios of 1:1 and 3:1 and 10% of the total disc mass in gas. In contrast to the collisionless case equal-mass mergers with gas do not result in very boxy remnants which is caused by the suppression of box orbits and the change of the projected shape of minor-axis tube orbits in the more axisymmetric remnants. The isophotal shape of 3:1 remnants and the global kinematic properties of 1:1 and 3:1 remnants are only weakly affected by the presence of gas. 1:1 remnants are slowly rotating whereas 3:1 remnants are fast rotating and discy. The shape of the stellar LOSVD is strongly influenced by gas. The LOSVDs of collisionless remnants have broad leading wings while their gaseous counterparts show steep leading wings, more consistent with observations of elliptical galaxies. We show that this change is also caused by the suppressed populating of box orbits and it is amplified by the formation of extended gas discs in the merger remnants. If elliptical galaxies have formed from mergers our results indicate that massive, slowly rotating boxy elliptical galaxies can not have formed from dissipative mergers of discs. Pure stellar (dry) mergers are the more likely candidates. On the other hand lower mass, fast rotating and discy ellipticals can have formed from dissipative (wet) mergers of early-type discs. So far, only unequal-mass disc mergers with gas can successfully explain their observed substructure. This is consistent with the revised morphological classification scheme of increasing importance of gas dissipation when moving from boxy ellipticals to discy ellipticals and then to spiral galaxies, proposed by Kormendy & Bender (abbreviated).Comment: accepted for publication by MNRA

Gambierol blocks a K+^+ current fraction without affecting catecholamine release in rat fetal adrenomedullary cultured chromaffin cells

International audienceGambierol inhibits voltage-gated K+ (KV) channels in various excitable and non-excitable cells. The purpose of this work was to study the effects of gambierol on single rat fetal (F19–F20) adrenomedullary cultured chromaffin cells. These excitable cells have different types of KV channels and release catecholamines. Perforated whole-cell voltage-clamp recordings revealed that gambierol (100 nM) blocked only a fraction of the total outward K$^+$ current and slowed the kinetics of K$^+$ current activation. The use of selective channel blockers disclosed that gambierol did not affect calcium-activated K$^+$ (KCa) and ATP-sensitive K$^+$ (KATP) channels. The gambierol concentration necessary to inhibit 50% of the K$^+$ current-component sensitive to the polyether (IC50) was 5.8 nM. Simultaneous whole-cell current-clamp and single-cell amperometry recordings revealed that gambierol did not modify the membrane potential following 11s depolarizing current-steps, in both quiescent and active cells displaying repetitive firing of action potentials, and it did not increase the number of exocytotic catecholamine release events, with respect to controls. The subsequent addition of apamin and iberiotoxin, which selectively block the KCa channels, both depolarized the membrane and enhanced by 2.7 and 3.5-fold the exocytotic event frequency in quiescent and active cells, respectively. These results highlight the important modulatory role played by KCa channels in the control of exocytosis from fetal (F19–F20) adrenomedullary chromaffin cells

Gambierol blocks a K+^+ current fraction and affects action potential duration and the firing rate in rat fetal chromaffin cells

The dinoflagellate genus Gambierdiscus, particularly Gambierdiscus toxicus is known to produce numerous ladder polycyclic ether compounds, including gambierol, characterized by a transfused octacyclic polyether core, as well as the identified ciguatoxins responsible for ciguatera poisoning. Gambierol inhibits voltage-gated K$^+$ (K$_V$) channels in various mammalian excitable and nonexcitable cells, and motor nerve terminals of the neuromuscular junction. In the present study, we investigated the action of gambierol on outward K$^+$ currents of cultured rat fetal adrenal medulla chromaffin cells using the whole-cell configuration voltage-clamp method. The pharmacological dissection of the outward K$^+$current, using selective K$^+$ channel inhibitors, revealed that gambierol reduced just a small fraction of the total outward current without affecting calcium-activated K$^+$ currents that were sensitive to apamin and iberiotoxin, and ATP-sensitive K$^+$ currents sensitive to glibenclamide. Cultured fetal chromaffin cells were excitable and generated either evoked (upon direct electric stimulation) or spontaneous action potentials. These action potentials were sensitive to tetrodotoxin that blocks voltage-gated Na$^+$(Na$_V$) channels. Gambierol neither affected the rising phase nor the overshoot of action potentials but significantly prolonged their repolarizing phase and increased the firing rate of action potentials during sustained current depolarization, as determined using current-clamp recordings. Our results highlight the effects of gambierol on K$_V$ channels and on the electrical properties of rat fetal chromaffin cells. It is likely that gambierol may cross the placental barrier as ciguatoxins do. Further studies are needed to determine whether such actions may have deleterious effects on fetuses

Gambierol effects on K(+) currents and catecholamine release in single rat fetal adrenomedullary cultured chromaffin cells

International audienceThe purpose of this work was to study the action of the polycyclic ether gambierol on K+ currents and catecholamine secretion in single rat fetal adrenomedullary cultured chromaffin (AMC) cells using perforated whole-cell voltage-clamp recordings, and current-clamp and electrochemical recordings. From the several types of voltage-gated K+ channels (KV) contributing to the total outward current of rat fetal AMC cells, gambierol only partly inhibited the total K+ current, when added after or before KCa and KATP blockers, and affected neither KCa nor KATP channels. After blocking of Nav and KATP channels, and preventing the activation of KCa channels, gambierol blocked 50% of the maximal K+ current fraction with an inhibitory concentration (IC50) of 5.8 ± 1.56 nM (n = 9). In marked contrast to ciguatoxins, gambierol slowed the kinetics of K+-current activation by 75.4 ± 10.1% (n = 4) with respect to controls (p = 0.031). Hence, before and after gambierol the activation time constants of K+ current were 3.82 ± 0.39 ms (n = 4) and 6.80 ± 1.02 ms (n = 4), respectively. Simultaneous current-clamp and single-cell amperometry recordings revealed that gambierol did not modify the membrane potential following 11-seconds depolarizing current-steps, in both quiescent and active cells displaying repetitive firing of action potentials, and it did not increase the number of exocytotic catecholamine release events, with respect to controls. The subsequent block of KCa channels, both depolarized the membrane and enhanced by 2.7 and 3.5-fold the exocytotic event frequency in quiescent and active cells respectively, highlighting the key modulatory role played by KCa channels in the control of exocytosis from rat fetal AMC cells

Gambierol blocks a K(+) current component affecting action potential duration in fetal adrenomedullary chromaffin cells. Is this action sufficient to modulate catecholamine release?

International audienceThe genera Gambierdiscus and Fukuyoa produce numerous ladder polycyclic ether compoundsincluding gambierol, characterized by a transfused octacyclic polyether core, and the identified ciguatoxins, responsible for ciguatera poisoning. Gambierol inhibits voltage-gated K+ (Kv) channels in various cells, and motor nerve terminals and enhances acetylcholine release. The purpose of this work was to study the effects of gambierol on cultured rat fetal adrenomedullary chromaffin cells. These excitable cells have different types of Kv channels and release catecholamines. Perforated patch-clamp current-recordings revealed that gambierol (100 nM) only blocked a small component of the total outward K+ current, and did not affect calciumâactivated K+ channels (KCa) and ATP-sensitive K+ (KATP) channels. When KATP and KCa channel activation were blocked, the gambierol concentration inhibiting 50 % of the K+ current-component (IC50) was 7.6 ± 1.10 nM (n = 9). Gambierol also slowed the kinetics of K+ current activation. The recording of all-or-none action potentials in chromaffin cells disclosed that gambierol (50 nM) prolonged by 33 % their repolarizing phase. Gambierol did not modify the membrane potential following 15-second depolarizing current-steps, and did not increase the number of exocytotic catecholamine release events, as determined by simultaneous patchclamp and single-cell amperometry recordings. Under, the same conditions gambierol enhanced catecholamine secretion provided KCa and KATP channels were blocked. In conclusion, the specific inhibition of Kv channels by gambierol is not enough to modulate catecholaminesecretion, emphasizing the key role played by KCa and KATP channels

A new omega-conotoxin that targets N-type voltage-sensitive calcium channels with unusual specificity.

A new specific voltage-sensitive calcium channel (VSCC) blocker has been isolated from the venom of the fish-hunting cone snail Conus consors. This peptide, named omega-Ctx CNVIIA, consists of 27 amino acid residues folded by 3 disulfide bridges. Interestingly, loop 4, which is supposed to be crucial for selectivity, shows an unusual sequence (SSSKGR). The synthesis of the linear peptide was performed using the Fmoc strategy, and the correct folding was achieved in the presence of guanidinium chloride, potassium buffer, and reduced/oxidized glutathione at 4 degrees C for 3 days. Both synthetic and native toxin caused an intense shaking activity, characteristic of omega-conotoxins targeting N-type VSCC when injected intracerebroventricularly to mice. Binding studies on rat brain synaptosomes revealed that the radioiodinated omega-Ctx CNVIIA specifically and reversibly binds to high-affinity sites with a K(d) of 36.3 pM. Its binding is competitive with omega-Ctx MVIIA at low concentration (K(i) = 2 pM). Moreover, omega-Ctx CNVIIA exhibits a clear selectivity for N-type VSCCs versus P/Q-type VSCCs targeted respectively by radioiodinated omega-Ctx GVIA and omega-Ctx MVIIC. Although omega-Ctx CNVIIA clearly blocked N-type Ca(2+) current in chromaffin cells, this toxin did not inhibit acetylcholine release evoked by nerve stimuli at the frog neuromuscular junction, in marked contrast to omega-Ctx GVIA. omega-Ctx CNVIIA thus represents a new selective tool for blocking N-type VSCC that displays a unique pharmacological profile and highlights the diversity of voltage-sensitive Ca(2+) channels in the animal kingdom

Congenital myasthenic syndrome caused by decreased receptor channel openings due to a novel mutation in the nicotinic acetylcholine receptor epsilon-subunit

Meeting Abstrac