scholarly journals Ion Channels Permeable to Monovalent and Divalent Cations: A Single-File Two-Site Channel Model.

2001 ◽  
Vol 51 (5) ◽  
pp. 569-576
Author(s):  
Yoshio Oosawa
Keyword(s):  
Ion Channels ◽  
Channel Model ◽  
Divalent Cations ◽  
Single File

scholarly journals Permeation of both cations and anions through a single class of ATP-activated ion channels in developing chick skeletal muscle.

1990 ◽  
Vol 95 (4) ◽  
pp. 569-590 ◽  
Author(s):  
S A Thomas ◽  
R I Hume
Keyword(s):  
Skeletal Muscle ◽  
Ion Channels ◽  
Divalent Cations ◽  
Reversal Potential ◽  
Noise Spectrum ◽  
Chloride Ions ◽  
Simultaneous Increase ◽  
Anion Channels ◽  
Patch Clamp Technique ◽  
Single Class

Micromolar concentrations of extracellular adenosine 5'-triphosphate (ATP) elicit a rapid excitatory response in developing chick skeletal muscle. Excitation is the result of a simultaneous increase in membrane permeability to sodium, potassium, and chloride ions. In the present study we quantify the selectivity of the ATP response, and provide evidence that a single class of ATP-activated ion channels conducts both cations and anions. Experiments were performed on myoballs using the whole-cell patch-clamp technique. We estimated permeability ratios by measuring the shift in reversal potential when one ion was substituted for another. We found that monovalent cations, divalent cations, and monovalent anions all permeate the membrane during the ATP response, and that there was only moderate selectivity between many of these ions. Calcium was the most permeant ion tested. To determine if ATP activates a single class of channels that conducts both cations and anions, or if ATP activates separate classes of cation and anion channels, we analyzed the fluctuations about the mean current induced by ATP. Ionic conditions were arranged so that the reversal potential for cations was +50 mV and the reversal potential for anions was -50 mV. Under these conditions, if ATP activates a single class of channels, ATP should not evoke an increase in noise at the reversal potential of the ATP current. However, if ATP activates separate classes of cation and anion channels, ATP should evoke a significant increase in noise at the reversal potential of the ATP current. At both +40 and -50 mV ATP elicited a clear increase in noise, but at the reversal potential of the ATP current (-5 mV), no increase in noise above background was seen. These results indicate that there is only a single class of excitatory ATP-activated channels, which do not select by charge. Based on analysis of the noise spectrum, the conductance of individual channels is estimated to be 0.2-0.4 pS.

Abstract P334: Biophysical Properties Of A Novel Mitochondrial Large Ubiquitous Non-selective Amiloride Sensitive (luna) Current

2021 ◽  
Vol 129 (Suppl_1) ◽  
Author(s):  
Enrique Balderas-Angeles ◽  
Thirupura Shankar ◽  
Anthony Balynas ◽  
Xue Yin ◽  
Dipayan Chaudhuri
Keyword(s):  
Ion Channels ◽  
Divalent Cations ◽  
Pressure Overload ◽  
Atp Synthesis ◽  
Intermembrane Space ◽  
Inner Mitochondrial Membrane ◽  
Patch Clamp Technique ◽  
Transport Chain ◽  
The Matrix ◽  
Established Cell

Inner mitochondrial membrane (IMM) ion channels and transporters account for communication of the matrix with the intermembrane space (IMS) and the cytosol. Transport of solutes and ions is keep under strict regulation mainly because small changes in solute concentrations could generate changes in mitochondrial volume or membrane potential (ΔΨ m ), interrupting ATP synthesis and leading to mitochondrial damage. The list of recently discovered mitochondrial ion channels has been growing in the past decades. In this work, using the patch-clamp technique we observed the activity of a novel mitochondrial current, named here LUNA current, in mitoplasts (IMM striped of outer membrane) from mouse liver, spleen, brain and heart, as well as established cell lines. LUNA is a novel non-selective cation current (K + >Na + >NMDG + >H + ) active at depolarized membrane potentials. The basal activity of whole-mitoplast LUNA currents from wild type mice hearts changed from 445±106 pA/pF to 1232±287 pA/pF upon chelation of external divalent cations (Ca 2+ and Mg 2+ ). Moreover, the activity of LUNA is independent of the mitochondrial Ca 2+ uniporter and of the non-selective reactive oxygen species modulator channel (ROMO1). In the heart, the activity of LUNA was enhanced in both the Tfam -KO mice, which have impaired electron transport chain (ETC) activity and are a model for mitochondrial cardiomyopathies, and mice with cardiac pressure overload due to transverse aortic constriction (TAC) compared to sham-operated hearts (729±197; n=7 vs 283±137 pA/pF). LUNA current is reversibly inhibited by amiloride with no sensitivity to the vast majority of common K + , Na + and Ca 2+ channels and ETC inhibitors. The molecular identity of mitochondrial LUNA current remains to be determined.

scholarly journals Crystal structures of a pentameric ion channel gated by alkaline pH show a widely open pore and identify a cavity for modulation

2018 ◽  
Vol 115 (17) ◽  
pp. E3959-E3968 ◽  
Author(s):  
Haidai Hu ◽  
Ákos Nemecz ◽  
Catherine Van Renterghem ◽  
Zaineb Fourati ◽  
Ludovic Sauguet ◽  
...  
Keyword(s):  
Ion Channels ◽  
Structural Information ◽  
Divalent Cations ◽  
Functional Characterization ◽  
Aromatic Amino Acids ◽  
Crystallographic Structure ◽  
Alkaline Ph ◽  
Quaternary Ammonium Ions ◽  
Gating Mechanism ◽  
The One

Pentameric ligand-gated ion channels (pLGICs) constitute a widespread class of ion channels, present in archaea, bacteria, and eukaryotes. Upon binding of their agonists in the extracellular domain, the transmembrane pore opens, allowing ions to go through, via a gating mechanism that can be modulated by a number of drugs. Even though high-resolution structural information on pLGICs has increased in a spectacular way in recent years, both in bacterial and in eukaryotic systems, the structure of the open channel conformation of some intensively studied receptors whose structures are known in a nonactive (closed) form, such as Erwinia chrysanthemi pLGIC (ELIC), is still lacking. Here we describe a gammaproteobacterial pLGIC from an endo-symbiont of Tevnia jerichonana (sTeLIC), whose sequence is closely related to the pLGIC from ELIC with 28% identity. We provide an X-ray crystallographic structure at 2.3 Å in an active conformation, where the pore is found to be more open than any current conformation found for pLGICs. In addition, two charged restriction rings are present in the vestibule. Functional characterization shows sTeLIC to be a cationic channel activated at alkaline pH. It is inhibited by divalent cations, but not by quaternary ammonium ions, such as tetramethylammonium. Additionally, we found that sTeLIC is allosterically potentiated by aromatic amino acids Phe and Trp, as well as their derivatives, such as 4-bromo-cinnamate, whose cocrystal structure reveals a vestibular binding site equivalent to, but more deeply buried than, the one already described for benzodiazepines in ELIC.

scholarly journals Calcium Modulation of Ligand Affinity in the Cyclic GMP–gated Ion Channels of Cone Photoreceptors

1997 ◽  
Vol 110 (5) ◽  
pp. 515-528 ◽  
Author(s):  
David H. Hackos ◽  
Juan I. Korenbrot
Keyword(s):  
Ion Channels ◽  
Divalent Cations ◽  
Amplitude Dependence ◽  
Cone Photoreceptors ◽  
Ligand Affinity ◽  
Average Value ◽  
Calcium Modulation ◽  
Endogenous Modulator ◽  
History Of ◽  
Gated Ion Channels

To investigate modulation of the activation of cGMP-gated ion channels in cone photoreceptors, we measured currents in membrane patches detached from the outer segments of single cones isolated from striped bass retina. The sensitivity of these channels to activation by cGMP depends on the history of exposure to divalent cations of the membrane's cytoplasmic surface. In patches maintained in 20 μM Ca++ and 100 μM Mg++ after excision, the current amplitude dependence on cGMP is well described by a Hill equation with average values of K1/2, the concentration necessary to activate half the maximal current, of 86 μM and a cooperativity index, n, of 2.57. Exposing the patch to a solution free of divalent cations irreversibly increases the cGMP sensitivity; the average value of K1/2 shifts to 58.8 μM and n shifts to 1.8. Changes in cGMP sensitivity do not affect other functional parameters of the ion channels, such as the interaction and permeation of mono- and divalent cations. Modulation of cGMP activation depends on the action of an endogenous factor that progressively dissociates from the channel as Ca++ concentration is lowered below 1 μM. The activity of the endogenous modulator is not well mimicked by exogenously added calmodulin, although this protein competes with the endogenous modulator for a common binding site. Thus, the modulation of cGMP affinity in cones depends on the activity of an unidentified molecule that may not be calmodulin.

scholarly journals In Intact Cone Photoreceptors, a Ca2+-dependent, Diffusible Factor Modulates the cGMP-gated Ion Channels Differently than in Rods

1998 ◽  
Vol 112 (5) ◽  
pp. 537-548 ◽  
Author(s):  
Tatiana I. Rebrik ◽  
Juan I. Korenbrot
Keyword(s):  
Ion Channels ◽  
Outer Segment ◽  
Divalent Cations ◽  
Cone Photoreceptors ◽  
Intact Cells ◽  
Channel Modulation ◽  
Dependent Change ◽  
Diffusible Factor ◽  
The Difference ◽  
Gated Ion Channels

We investigated the modulation of cGMP-gated ion channels in single cone photoreceptors isolated from a fish retina. A new method allowed us to record currents from an intact outer segment while controlling its cytoplasmic composition by superfusion of the electropermeabilized inner segment. The sensitivity of the channels to agonists in the intact outer segment differs from that measured in membrane patches detached from the same cell. This sensitivity, measured as the ligand concentration necessary to activate half-maximal currents, K1/2, also increases as Ca2+ concentration decreases. In electropermeabilized cones, K1/2 for cGMP is 335.5 ± 64.4 μM in the presence of 20 μM Ca2+, and 84.3 ± 12.6 μM in its absence. For 8Br-cGMP, K1/2 is 72.7 ± 11.3 μM in the presence of 20 μM Ca2+ and 15.3 ± 4.5 μM in its absence. The Ca2+-dependent change in agonist sensitivity is larger in extent than that measured in rods. In electropermeabilized tiger salamander rods, K1/2 for 8Br-cGMP is 17.9 ± 3.8 μM in the presence of 20 μM Ca2+ and 7.2 ± 1.2 μM in its absence. The Ca2+-dependent modulation is reversible in intact cone outer segments, but is progressively lost in the absence of divalent cations, suggesting that it is mediated by a diffusible factor. Comparison of data in intact cells and detached membrane fragments from cones indicates that this factor is not calmodulin. At 40 μM 8Br-cGMP, the Ca2+-dependent change in sensitivity in cones is half-maximal at KCa = 286 ± 66 nM Ca2+. In rods, by contrast, KCa is ∼50 nM Ca2+. The difference in magnitude and Ca2+ dependence of channel modulation between photoreceptor types suggests that this modulation may play a more significant role in the regulation of photocurrent gain in cones than in rods.

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