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Ion/ion reactions with "onium" reagents: an approach for the gas-phase transfer of organic cations to multiply-charged anions.
Gilbert JD, Prentice BM, McLuckey SA
(2015) J Am Soc Mass Spectrom 26: 818-25
MeSH Terms: Alkylation, CME-Carbodiimide, Catalysis, Chelating Agents, Cross-Linking Reagents, Edetic Acid, Energy Transfer, Hot Temperature, Indicators and Reagents, Models, Molecular, Oligopeptides, Organophosphorus Compounds, Protein Conformation, Quaternary Ammonium Compounds, Spectrometry, Mass, Electrospray Ionization, Static Electricity, Sulfonium Compounds, Tandem Mass Spectrometry, Tetraethylammonium, Volatilization
Show Abstract · Added August 17, 2016
The use of ion/ion reactions to effect gas-phase alkylation is demonstrated. Commonly used fixed-charge "onium" cations are well-suited for ion/ion reactions with multiply deprotonated analytes because of their tendency to form long-lived electrostatic complexes. Activation of these complexes results in an SN2 reaction that yields an alkylated anion with the loss of a neutral remnant of the reagent. This alkylation process forms the basis of a general method for alkylation of deprotonated analytes generated via electrospray, and is demonstrated on a variety of anionic sites. SN2 reactions of this nature are demonstrated empirically and characterized using density functional theory (DFT). This method for modification in the gas phase is extended to the transfer of larger and more complex R groups that can be used in later gas-phase synthesis steps. For example, N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide (CMC) is used to transfer a carbodiimide functionality to a peptide anion containing a carboxylic acid. Subsequent activation yields a selective reaction between the transferred carbodiimide group and a carboxylic acid, suggesting the carbodiimide functionality is retained through the transfer process. Many different R groups are transferable using this method, allowing for new possibilities for charge manipulation and derivatization in the gas phase.
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20 MeSH Terms
A model of action potentials and fast Ca2+ dynamics in pancreatic beta-cells.
Fridlyand LE, Jacobson DA, Kuznetsov A, Philipson LH
(2009) Biophys J 96: 3126-39
MeSH Terms: Action Potentials, Adenosine Triphosphate, Animals, Calcium, Calcium Channels, L-Type, Calcium Signaling, Cell Membrane, Computer Simulation, Delayed Rectifier Potassium Channels, Glucose, Insulin-Secreting Cells, Mice, Mice, Knockout, Models, Neurological, Patch-Clamp Techniques, Potassium, Potassium Channels, Voltage-Gated, Shab Potassium Channels, Sodium, Tetraethylammonium, Time
Show Abstract · Added February 12, 2015
We examined the ionic mechanisms mediating depolarization-induced spike activity in pancreatic beta-cells. We formulated a Hodgkin-Huxley-type ionic model for the action potential (AP) in these cells based on voltage- and current-clamp results together with measurements of Ca(2+) dynamics in wild-type and Kv2.1 null mouse islets. The model contains an L-type Ca(2+) current, a "rapid" delayed-rectifier K(+) current, a small slowly-activated K(+) current, a Ca(2+)-activated K(+) current, an ATP-sensitive K(+) current, a plasma membrane calcium-pump current and a Na(+) background current. This model, coupled with an equation describing intracellular Ca(2+) homeostasis, replicates beta-cell AP and Ca(2+) changes during one glucose-induced spontaneous spike, the effects of blocking K(+) currents with different inhibitors, and specific complex spike in mouse islets lacking Kv2.1 channels. The currents with voltage-independent gating variables can also be responsible for burst behavior. Original features of this model include new equations for L-type Ca(2+) current, assessment of the role of rapid delayed-rectifier K(+) current, and Ca(2+)-activated K(+) currents, demonstrating the important roles of the Ca(2+)-pump and background currents in the APs and bursts. This model provides acceptable fits to voltage-clamp, AP, and Ca(2+) concentration data based on in silico analysis.
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21 MeSH Terms
A potassium channel blocker induces a long-lasting enhancement of corticostriatal responses.
Norman ED, Egli RE, Colbran RJ, Winder DG
(2005) Neuropharmacology 48: 311-21
MeSH Terms: Animals, Cerebral Cortex, Corpus Striatum, Dose-Response Relationship, Drug, Excitatory Postsynaptic Potentials, In Vitro Techniques, Potassium Channel Blockers, Rats, Rats, Sprague-Dawley, Tetraethylammonium, Time Factors
Show Abstract · Added May 19, 2014
Disruptions in synaptic plasticity in the dorsal striatum may contribute to the pathophysiology underlying Parkinson's disease. Here we report a novel, chemically-induced form of plasticity induced by application of the potassium channel blocker tetraethylammonium (TEA) in the dorsolateral striatum of the adult rat. Transient application of TEA persistently increased synaptically-evoked extracellularly-recorded corticostriatal responses in an activity-, concentration- and time-dependent manner. Pharmacological experiments suggest that this plasticity is dependent on L-type calcium channel and protein kinase C (PKC) activation. Striatal dopamine depletion induced by nigrostriatal dopamine lesions with 6-hydroxydopamine significantly reduced, but did not abolish, TEA-mediated enhancement of the corticostriatal response. Intracellular recordings demonstrate that this TEA-mediated plasticity is associated with an increase in EPSP size and slope, as well as input resistance. Collectively, these findings demonstrate a novel form of L-type calcium channel-dependent plasticity in the adult dorsal striatum that is induced in the absence of dopaminergic input.
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11 MeSH Terms
Effect of firing rate on the calcium permeability in adult neurons during spontaneous action potentials.
Mazzanti M, Galli A, Ferroni A
(1992) Biophys J 63: 926-34
MeSH Terms: Action Potentials, Animals, Calcium, Calcium Channels, Cells, Cultured, Electrophysiology, Ganglia, Spinal, Ion Channel Gating, Kinetics, Neurons, Rats, Tetraethylammonium, Tetraethylammonium Compounds, Time Factors
Show Abstract · Added February 19, 2015
Calcium channels in neurons mediate a wide variety of essential functions. In addition to contributing to action potential shape, they furnish a substrate that acts as an intracellular second messenger. This study shows that the shape of the neuronal action potential has characteristics that promote long openings of L-type (high threshold) calcium channels. We also present evidence that a change in the firing rate of isolated neurons modulates gating of single calcium channels. This mechanism could be important in modulating neuron excitability and providing a rise in intracellular Ca, when needed.
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14 MeSH Terms