| 1. |
- Anand, Deepak, et al.
(författare)
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Grease in the Nucleus : Insights into the Dynamic Life of Nuclear Membranes
- 2023
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Ingår i: Journal of Membrane Biology. - : Springer Science and Business Media LLC. - 0022-2631 .- 1432-1424. ; 256:2, s. 137-145
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Forskningsöversikt (refereegranskat)abstract
- Nucleus is at the center stage of cellular drama orchestrated in the life of a cell and the nucleoplasm is surrounded by a double membranous compartment constituting the Nuclear membrane/envelope (NE) that separates it from the cytoplasm in nucleated cells. The initial understanding of the NE was that of a border security entity between the nucleus and the cytoplasm, separating gene regulation and transcription in the nucleus from translation in the cytoplasm. However, the discovery of a wide array of inherited diseases caused by mutations in genes encoding proteins that reside or interact with NE diverted the interest into deciphering the lipid-protein-rich environment of the NE. Today, the NE is considered a dynamic organelle which forms a functional linkage between the nucleus and the rest of the cell. The exposure of NE to constant mechanical constraints by its connectivity to the large polymer network of the lamina and chromatin on one side, and to the cytoskeleton on the other side results, in a variety of shape changes. We discuss two such deformation, the formation of nuclear blebs and nucleoplasmic reticulum (NER). Although the protein and the lipid composition of NE comprises a small fraction of the total lipid-protein load of the cell, the ability to define the lipid-protein composition of Inner nuclear membrane (INM) and Outer nuclear membrane (ONM) with precision is crucial for obtaining a deeper mechanistic understanding of their lipid-protein interaction and the various signaling pathways that are triggered by them. In addition, this allows us to further understand the direct and indirect roles of NE machinery in the chromosomal organization and gene regulation.
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| 2. |
- Andersson, Alma E. V., et al.
(författare)
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Exploring the Viral Channel Kcv(PBCV-1) Function via Computation
- 2018
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Ingår i: Journal of Membrane Biology. - : SPRINGER. - 0022-2631 .- 1432-1424. ; 251:3, s. 419-430
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Tidskriftsartikel (refereegranskat)abstract
- Viral potassium channels (Kcv) are homologous to the pore module of complex -selective ion channels of cellular organisms. Due to their relative simplicity, they have attracted interest towards understanding the principles of conduction and channel gating. In this work, we construct a homology model of the open state, which we validate by studying the binding of known blockers and by monitoring ion conduction through the channel. Molecular dynamics simulations of this model reveal that the re-orientation of selectivity filter carbonyl groups coincides with the transport of potassium ions, suggesting a possible mechanism for fast gating. In addition, we show that the voltage sensitivity of this mechanism can originate from the relocation of potassium ions inside the selectivity filter. We also explore the interaction of with the surrounding bilayer and observe the binding of lipids in the area between two adjacent subunits. The model is available to the scientific community to further explore the structure/function relationship of Kcv channels.
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| 3. |
- Birnir, Bryndis, et al.
(författare)
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A structural determinant of desensitization and allosteric regulation by pentobarbitone of the GABAA receptor.
- 1997
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 155:2, s. 157-66
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Tidskriftsartikel (refereegranskat)abstract
- Functional properties of the alpha1beta1 GABAA receptor changes in a subunit-specific manner when a threonine residue in the M2 region at the 12' position was mutated to glutamine. The rate and extent of desensitization increased in all mutants but the rate of activation was faster in the beta1 mutants. A negligible plateau current and abolition of potentiation by pentobarbitone of the GABA-activated current depended on the Thr 12' Gln mutation being present in the beta1 subunit. The Hill coefficient of the peak current response to GABA was reduced to less than one also in a beta1 subunit-specific manner. It was concluded that the beta1 subunit dominated conformational changes activated by GABA.
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| 4. |
- Birnir, Bryndis, et al.
(författare)
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Characteristics of GABAA channels in rat dentate gyrus.
- 1994
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 142:1, s. 93-102
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Tidskriftsartikel (refereegranskat)abstract
- Single channel currents were activated by GABA (0.5 to 5 microM) in cell-attached and inside-out patches from cells in the dentate gyrus of rat hippocampal slices. The currents reversed at the chloride equilibrium potential and were blocked by bicuculline (100 microM). Several different kinds of channel were seen: high conductance and low conductance, rectifying and "nonrectifying." Channels had multiple conductance states. The open probability (Po) of channels was greater at depolarized than at hyperpolarized potentials and the relationship between Po and potential could be fitted with a Boltzmann equation with equivalent valency (z) of 1. The combination of outward rectification and potential-dependent open probability gave very little chloride current at hyperpolarized potentials but steeply increasing current with depolarization, useful properties for a tonic inhibitory mechanism.
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| 5. |
- Birnir, Bryndis, et al.
(författare)
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GABA concentration sets the conductance of delayed GABAA channels in outside-out patches from rat hippocampal neurons.
- 2001
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 181:3, s. 171-83
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Tidskriftsartikel (refereegranskat)abstract
- GABAA channels were activated by GABA in outside-out patches from rat cultured hippocampal neurons. They were blocked by bicuculline and potentiated by diazepam. In 109 of 190 outside-out patches, no channels were active before exposure to GABA (silent patches). The other 81 patches showed spontaneous channel activity. In patches containing spontaneous channel activity, rapid application of GABA rapidly activated channels. In 93 of the silent patches, channels could be activated by GABA but only after a delay that was sometimes as long as 10 minutes. The maximum channel conductance of the channels activated after a delay increased with GABA concentration from less than 10 pS (0.5 microm GABA) to more than 100 pS (10 mm GABA). Fitting the data with a Hill-type equation gave an EC50 value of 33 microm and a Hill coefficient of 0.6. The channels showed outward rectification and were chloride selective. In the presence of 1 microm diazepam, the GABA EC50 decreased to 0.2 microm but the maximum conductance was unchanged. Diazepam decreased the average latency for channel opening. Bicuculline, a GABA antagonist, caused a concentration-dependent decrease in channel conductance. In channels activated with 100 microm GABA the bicuculline IC50 was 19 microm. The effect of GABA on channel conductance shows that the role of the ligand in GABAA receptor channel function is more complex than previously thought.
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| 6. |
- Birnir, Bryndis, et al.
(författare)
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Rapid desensitization of alpha 1 beta 1 GABA A receptors expressed in Sf9 cells under optimized conditions.
- 1995
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 148:2, s. 193-202
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Tidskriftsartikel (refereegranskat)abstract
- alpha 1 and beta 1 subunits of human GABA A receptors were expressed in Sf9 cells using the Sf9-baculovirus system. Better expression was obtained by manipulating the system. Cell growth phase at the time of infection determined the practical range of virus titre, the period postinfection during which cells were useful for signal detection and the maximal current obtained. Cells in the early exponential phase were relatively insensitive to multiplicity of infection (MOI) whereas cells in the mid- to late-exponential phase were highly dependent on MOI and they responded with the largest Cl- current generated by GABA. Channels activated by GABA were chloride-selective. Half the maximum peak whole-cell current was obtained with 11 microM GABA. The time course of Cl- currents activated by saturating GABA concentrations in cells infected with alpha 1 beta 1-recombinant viruses was examined employing a rapid perfusion system which allowed whole-cell solution exchange in less than 1 msec. The current decay could be fitted by 3 to 4 exponentials for the first 8 sec. The initial fast current decrease had a time constant of about 23 msec. No voltage dependence of time constants was detected but the whole-cell IV relation showed outward rectification. Currents were depressed by bicuculline, penicillin and picrotoxin and potentiated by pentobarbitone.
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| 7. |
- Birnir, Bryndis, et al.
(författare)
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Spontaneously opening GABA(A) channels in CA1 pyramidal neurones of rat hippocampus.
- 2000
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 174:1, s. 21-9
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Tidskriftsartikel (refereegranskat)abstract
- Spontaneous, single channel, chloride currents were recorded in 48% of cell-attached patches on neurones in the CA1 region of rat hippocampal slices. In some patches, there was more than 1 channel active. They showed outward rectification: both channel conductance and open probability were greater at depolarized than at hyperpolarized potentials. Channels activated by gamma-aminobutyric acid (GABA) in silent patches on the same neurones had similar conductance and outward rectification. The spontaneous currents were inhibited by bicuculline and potentiated by diazepam. It was concluded that the spontaneously opening channels were constitutively active, nonsynaptic GABA(A) channels. Such spontaneously opening GABA(A) channels may provide a tonic inhibitory mechanism in these cells and perhaps in other cells that have GABA(A) receptors although not having a GABA(A) synaptic input. They may also be a target for clinically useful drugs such as the benzodiazepines.
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| 8. |
- Copello, J A, et al.
(författare)
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Differential activation by Ca2+, ATP and caffeine of cardiac and skeletal muscle ryanodine receptors after block by Mg2+.
- 2002
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Ingår i: Journal of Membrane Biology. - : Springer Science and Business Media LLC. - 0022-2631 .- 1432-1424. ; 187:1, s. 51-64
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Tidskriftsartikel (refereegranskat)abstract
- The block of rabbit skeletal ryanodine receptors (RyR1) and dog heart RyR2 by cytosolic [Mg2+], and its reversal by agonists Ca2+, ATP and caffeine was studied in planar bilayers. Mg2+ effects were tested at submaximal activating [Ca2+] (5 microM). Approximately one third of the RyR1s had low open probability ("LA channels") in the absence of Mg2+. All other RyR1s displayed higher activity ("HA channels"). Cytosolic Mg2+ (1 mM) blocked individual RyR1 channels to varying degrees (32 to 100%). LA channels had residual P(o) <0.005 in 1 mM Mg2+ and reactivated poorly with [Ca2+] (100 microM), caffeine (5 mM), or ATP (4 mM; all at constant 1 mM Mg2+). HA channels had variable activity in Mg2+ and variable degree of recovery from Mg2+ block with Ca2+, caffeine or ATP application. Nearly all cardiac RyR2s displayed high activity in 5 microM [Ca2+]. They also had variable sensitivity to Mg2+. However, the RyR2s consistently recovered from Mg2+ block with 100 microM [Ca2+] or caffeine application, but not when ATP was added. Thus, at physiological [Mg2+], RyR2s behaved as relatively homogeneous Ca2+/caffeine-gated HA channels. In contrast, RyR1s displayed functional heterogeneity that arises from differential modulatory actions of Ca2+ and ATP. These differences between RyR1 and RyR2 function may reflect their respective roles in muscle physiology and excitation-contraction coupling.
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| 9. |
- Cournia, Zoe, et al.
(författare)
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Membrane Protein Structure, Function, and Dynamics : a Perspective from Experiments and Theory
- 2015
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Ingår i: Journal of Membrane Biology. - : Springer. - 0022-2631 .- 1432-1424. ; 248:4, s. 611-640
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Tidskriftsartikel (refereegranskat)abstract
- Membrane proteins mediate processes that are fundamental for the flourishing of biological cells. Membrane-embedded transporters move ions and larger solutes across membranes; receptors mediate communication between the cell and its environment and membrane-embedded enzymes catalyze chemical reactions. Understanding these mechanisms of action requires knowledge of how the proteins couple to their fluid, hydrated lipid membrane environment. We present here current studies in computational and experimental membrane protein biophysics, and show how they address outstanding challenges in understanding the complex environmental effects on the structure, function, and dynamics of membrane proteins.
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| 10. |
- Curmi, J P, et al.
(författare)
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The influence of membrane potential on chloride channels activated by GABA in rat cultured hippocampal neurons.
- 1993
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 136:3, s. 273-80
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Tidskriftsartikel (refereegranskat)abstract
- Chloride currents were activated by a low concentration of GABA (0.5 microM) in neonatal rat hippocampal neurons cultured for up to 14 days. Currents elicited by 0.5 microM GABA in neurons, voltage-clamped using the whole-cell technique with pipettes containing 149 mM Cl-, reversed close to 0 mV whether pipettes contained 144 mM Na+ or 140 mM Cs+, and were blocked by 100 microM bicuculline. Current-voltage curves showed outward rectification. Single channel currents appeared in cell-attached patches when the pipette tip was perfused with pipette solution containing 0.5 microM GABA and disappeared when a solution containing 100 microM bicuculline plus 0.5 microM GABA was injected into the pipette tip. The channels showed outward rectification and, in some patches, had a much lower probability of opening at hyperpolarized potentials. The average chord conductance in 10 patches hyperpolarized by 80 mV was 7.8 +/- 1.6 pS (SEM) compared with a chord conductance of 34.1 +/- 3.5 pS (SEM) in the same patches depolarized by 80 mV. Similar single channel currents were also activated in cell-free, inside-out patches in symmetrical chloride solutions when 0.5 microM GABA was injected into the pipette tip. The channels showed outward rectification similar to that seen in cell-attached patches, and some channels had a lower probability of opening at hyperpolarized potentials. The average chord conductance in 13 patches hyperpolarized by 80 mV was 11.8 +/- 2.3 pS (SEM) compared with 42.1 +/- 3.1 pS (SEM) in the same patches depolarized by 80 mV.
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