scholarly journals A voltage‐dependent depolarization induced by low external glucose in neurons of the nucleus of the tractus solitarius: interaction with K ATP channels

2019 ◽  
Vol 597 (9) ◽  
pp. 2515-2532 ◽  
Author(s):  
Cahuê Bernardis Murat ◽  
Ricardo Mauricio Leão
Keyword(s):  
Voltage Dependent ◽  
External Glucose

scholarly journals A voltage-dependent depolarization induced by low external glucose in neurons of the nucleus of the tractus solitarius of rats: interaction with KATP channels regulated by external glucose.

2018 ◽  
Author(s):  
Cahue de Bernardis Murat ◽  
Ricardo Leao
Keyword(s):  
Membrane Potential ◽  
Glucose Solution ◽  
Reversal Potential ◽  
Membrane Hyperpolarization ◽  
Cationic Current ◽  
Voltage Dependent ◽  
Extracellular Glucose ◽  
Low Glucose ◽  
External Glucose

The brainstem nucleus of the tractus solitarius (NTS) is an integrative center for autonomic counterregulatory responses to hypoglycemia, NTS neurons can also sense fluctuations in extracellular glucose levels altering their membrane potential. KATP channels links the metabolic status of the neuron to its excitability, but the role of KATP channels in controlling NTS neurons excitability and in sensing extracellular glucose changes is not clear. Here we investigated using in vitro electrophysiological recordings in brainstem slices the influence of KATP channels on the membrane potential of NTS neurons in normoglicemic and hyperglycemic external glucose concentrations, and after switching the external glucose to a hypoglycemic level. We found that in normoglicemic (5 mM) external glucose application of tolbutamide, a KATP blocker, induced a substantial depolarization of most NTS neurons, while application of diazoxide, a KATP opener, hyperpolarized the membrane of all NTS neurons. Interestingly, neurons not responsive to tolbutamide were more depolarized than responsive neurons. In a hyperglycemic solution (10 mM glucose) few neurons depolarized in response to tolbutamide. We found that these neurons were more depolarized than neurons in 5 mM glucose and only the more hyperpolarized responded to tolbutamide. The non-responsive neurons did not respond to tolbutamide even when hyperpolarized. Interestingly application of a low-gucose solution (0.5 mM) did not hyperpolarized the RMP but produced a depolarization in most neurons. This effect was voltage-dependent not seen in neurons more depolarized, but could be observed when the neurons were hyperpolarized. Depolarization by tolbutamide avoided further depolarization by low glucose, unless the membrane was hyperpolarized. Application of 0.5 mM glucose solution in neurons incubated in 10 mM glucose depolarized the membrane only in more hyperpolarized neurons, which responded to tolbutamide, or after membrane hyperpolarization. The effect of glucose was caused by activation of a cationic current with a reversal potential around the potential were the neurons were non-responsive to low glucose. We conclude that NTS neurons present KATP channels open at rest in normoglicemic conditions, and that their state is affected by extracellular glucose. Moreover, NTS neurons depolarize the membrane in response to the application of a low-glucose solution, but this effect is occluded by membrane depolarization triggered by KATP blockage. This suggests a homeostatic regulation of the membrane potential by glucose and a possible mechanism related to hypoglycemia-associated autonomic failure.

The low-resolution 3D-structure of porin, a channel-forming protein in E. coliouter membranes

1983 ◽  
Vol 41 ◽  
pp. 440-441
Author(s):  
A. Engel ◽  
D.L. Dorset ◽  
A. Massalski ◽  
J.P. Rosenbusch
Keyword(s):  
Crystal Packing ◽  
3D Structure ◽  
Gram Negative Bacteria ◽  
Protein Ratio ◽  
Crystal Forms ◽  
Large Molecules ◽  
Functional Studies ◽  
Voltage Dependent ◽  
Planar Membranes ◽  
Hexagonal Arrays

Porins represent a group of channel forming proteins that facilitate diffusion of small solutes across the outer membrane of Gram-negative bacteria, while excluding large molecules (>650 Da). Planar membranes reconstituted from purified matrix porin (OmpF protein) trimers and phospholipids have allowed quantitative functional studies of the voltage-dependent channels and revealed concerted activation of triplets. Under the same reconstitution conditions but using high protein concentrations porin aggregated to 2D lattices suitable for electron microscopy and image processing. Depending on the lipid-to- protein ratio three different crystal packing arrangements were observed: a large (a = 93 Å) and a small (a = 79 Å) hexagonal and a rectangular (a = 79 Å b = 139 Å) form with p3 symmetry for the hexagonal arrays. In all crystal forms distinct stain filled triplet indentations could be seen and were found to be morphologically identical within a resolution of (22 Å). It is tempting to correlate stain triplets with triple channels, but the proof of this hypothesis requires an analysis of the structure in 3 dimensions.

Cryo-Electron Microscopy and Correlation Averaging of Frozen-Hydrated, Polymorphic 2D Crystals of the Mitochondrial Outer Membrane Channel

1990 ◽  
Vol 48 (1) ◽  
pp. 100-101
Author(s):  
Xiao-Wei Guo
Keyword(s):  
Outer Membrane ◽  
Hexagonal Lattice ◽  
Mitochondrial Outer Membrane ◽  
Rectangular Lattice ◽  
Electron Microscopic ◽  
Cryo Electron Microscopy ◽  
Voltage Dependent ◽  
Outer Membrane Channel ◽  
2D Crystals ◽  
Vdac Channel

Voltage-dependent, anion-selective channels (VDAC) are formed in the mitochondrial outer membrane (mitOM) by a 30-kDa polypeptide. These channels form ordered 2D arrays when mitOMs from Neurospora crassa are treated with soluble phospholipase A2. We obtain low-dose electron microscopic images of unstained specimens of VDAC crystals preserved in vitreous ice, using a Philips EM420 equipped with a Gatan cryo-transfer stage. We then use correlation analysis to compute average projections of the channel crystals. The procedure involves Fourier-filtration of a region within a crystal field to obtain a preliminary average that is subsequently cross-correlated with the entire crystal. Subregions are windowed from the crystal image at coordinates of peaks in the cross-correlation function (CCF, see Figures 1 and 2) and summed to form averages (Figure 3).The VDAC channel forms several different types of crystalline arrays in mitOMs. The polymorph first observed during phospholipase treatment is a parallelogram array (a=13 run, b=11.5 run, θ==109°) containing 6 water-filled pores per unit cell. Figure 1 shows the CCF of a sub-field of such an “oblique” array used to compute the correlation average of Figure 3A. With increased phospholipase treatment, other polymorphs are observed, often co-existing within the same crystal. For example, two distinct (but closely related) types of lattices occur in the field corresponding to the CCF of Figure 2: a “contracted” version of the parallelogram lattice (a=13 run, b=10 run, θ=99°), and a near-rectangular lattice (a=8.5 run, b=5 nm). The pattern of maxima in this CCF suggests that a third, near-hexagonal lattice (a=4.5 nm) may also be present. The correlation averages of Figures 3B-D were computed from polycrystalline fields, using peak coordinates in regions of CCFs corresponding to each of the three lattice types.

Role of the Cilia Membrane in Control of Microtubule Sliding

1980 ◽  
Vol 38 ◽  
pp. 612-615
Author(s):  
Edna S. Kaneshiro
Keyword(s):  
Control Mechanism ◽  
Beat Frequency ◽  
Surface Membrane ◽  
Ciliary Membrane ◽  
Ciliary Beating ◽  
Ciliary Reversal ◽  
Voltage Dependent ◽  
Reversal Mechanism ◽  
And Function

It is currently believed that ciliary beating results from microtubule sliding which is restricted in regions to cause bending. Cilia beat can be modified to bring about changes in beat frequency, cessation of beat and reversal in beat direction. In ciliated protozoans these modifications which determine swimming behavior have been shown to be related to intracellular (intraciliary) Ca2+ concentrations. The Ca2+ levels are in turn governed by the surface ciliary membrane which exhibits increased Ca2+ conductance (permeability) in response to depolarization. Mutants with altered behaviors have been isolated. Pawn mutants fail to exhibit reversal of the effective stroke of ciliary beat and therefore cannot swim backward. They lack the increased inward Ca2+ current in response to depolarizing stimuli. Both normal and pawn Paramecium made leaky to Ca2+ by Triton extrac¬tion of the surface membrane exhibit backward swimming only in reactivating solutions containing greater than IO-6 M Ca2+ Thus in pawns the ciliary reversal mechanism itself is left operational and only the control mechanism at the membrane is affected. The topographic location of voltage-dependent Ca2+ channels has been identified as a component of the ciliary mem¬brane since the inward Ca2+ conductance response is eliminated by deciliation and the return of the response occurs during cilia regeneration. Since the ciliary membrane has been impli¬cated in the control of Ca2+ levels in the cilium and therefore is the site of at least one kind of control of microtubule sliding, we have focused our attention on understanding the structure and function of the membrane.

Analysis of the Bias Dependent Spectral Response of a-SiC:H p-i-n Photodiode

2002 ◽  
Vol 715 ◽  
Author(s):  
P. Louro ◽  
A. Fantoni ◽  
Yu. Vygranenko ◽  
M. Fernandes ◽  
M. Vieira
Keyword(s):  
Bias Voltage ◽  
Voltage Dependence ◽  
Spectral Response ◽  
Surface Recombination ◽  
Electrical Field ◽  
Field Reversal ◽  
Current Voltage ◽  
Voltage Dependent ◽  
And Inversion ◽  
Device Operation

AbstractThe bias voltage dependent spectral response (with and without steady state bias light) and the current voltage dependence has been simulated and compared to experimentally obtained values. Results show that in the heterostructures the bias voltage influences differently the field and the diffusion part of the photocurrent. The interchange between primary and secondary photocurrent (i. e. between generator and load device operation) is explained by the interaction of the field and the diffusion components of the photocurrent. A field reversal that depends on the light bias conditions (wavelength and intensity) explains the photocurrent reversal. The field reversal leads to the collapse of the diode regime (primary photocurrent) launches surface recombination at the p-i and i-n interfaces which is responsible for a double-injection regime (secondary photocurrent). Considerations about conduction band offsets, electrical field profiles and inversion layers will be taken into account to explain the optical and voltage bias dependence of the spectral response.

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