OBJECTIVE: To construct a three-dimensional structural model for the selectivity filter in the transient receptor pontential melastatin 8 (TRPM8) ion channel. METHODS: In the Rosetta computational structural biology suite, multiple rounds of modeling with the kinematic loop closure algorithm were performed. RESULTS: After nine rounds of computational modeling, we obtained the models of the selectivity filter within the TRPM8 channel with the lowest energy and high convergence. The model showed that the sidechain of D918 points were away from the central ion permeation pathway, while the sidechains of Q914, D920 and T923 pointed towards it. The glycosylation site N934 was located outside the pore region and its side chain directed to the extracellular water environment. CONCLUSIONS A three-dimensional structural model for the selectivity filter in the TRPM8 ion channel was constructed, which provides reliable structural information for exploring the mechanism of ion selectivity.
Algorithms ; Ion Channel Gating ; Models, Molecular ; TRPM Cation Channels ; chemistry

Ion channels mediate ion transport across membranes, and play vital roles in processes of matter exchange, energy transfer and signal transduction in living organisms. Recently, structural studies of ion channels have greatly advanced our understanding of their ion selectivity and gating mechanisms. Structural studies of voltage-gated potassium channels elucidate the structural basis for potassium selectivity and voltage-gating mechanism; structural studies of voltage-gated sodium channels reveal their slow and fast inactivation mechanisms; and structural studies of transient receptor potential (TRP) channels provide complex and diverse structures of TRP channels, and their ligand gating mechanisms. In the article we summarize recent progress on ion channel structural biology, and outlook the prospect of ion channel structural biology in the future.
Ion Channel Gating ; physiology ; Ion Channels ; Voltage-Gated Sodium Channels ; chemistry ; metabolism

The history and current situation of cell membrane ion-channel gating mechanism study were reviewed, with an emphasis on the application and the latest developments of kinetic model in gating mechanism study; the problems in present study and ion-channel gating mechanism kinetics model for future investigations were finally discussed.
Cell Membrane ; physiology ; Humans ; Ion Channel Gating ; Kinetics ; Models, Biological ; Research ; trends

BACKGROUNDFew studies have explored the inward sodium current (INa) kinetics of transitional cardiomyocytes. This study aimed to explore the kinetics of transitional cardiomyocytes types alpha and beta.

METHODSThe whole-cell patch clamp technique was used to study the rapid INa of isolated transitional cardiomyocytes in the Koch triangle of rabbit hearts.

RESULTSMaximal amplitude and density of INa in type alpha and type beta was (-1627 +/- 288) pA (alpha), (-35.17 +/- 6.56) pA/pF (beta) and (-3845 +/- 467) pA (alpha), (-65.64 +/- 10.23) pA/pF (beta) (P < 0.05). Steady state activation curves of INa, fitted to a Boltzmann distribution for both types, were sigmoid in shape. Half activation voltage and slope factors did not significantly differ between types at (-43.46 +/- 0.85) mV (alpha), (-41.39 +/- 0.47) mV (beta) or (9.04 +/- 0.66) mV (alpha), (11.08 +/- 0.89) mV (beta). Steady state inactivation curves of INa, fitted to a Boltzmann distribution in both types were inverse "S" shape. Half inactivation voltage and slope factors were (-109.9 +/- 0.62) mV (alpha), (-107.5 +/- 0.49) mV (beta) and (11.78 +/- 0.36) mV (alpha), (11.57 +/- 0.27) mV(beta), (P > 0.05), but time constants of inactivation were significantly different at (1.10 +/- 0.19) mV (alpha) and (2.37 +/- 0.33) ms (beta), (P < 0.05). Time constants of recovery from inactivation of INa for both types were (122.16 +/- 27.43) mV (alpha) and (103.84 +/- 28.97) ms (beta) (P < 0.05).

CONCLUSIONSTransitional cardiomyocytes in rabbit hearts show a heterogeneous, voltage gated and time dependent fast inward sodium current. Types alpha and beta show the features of INa similar to those in slow- and fast-response myocytes, with probably better automaticity and conductivity, respectively.

Animals ; Female ; Ion Channel Gating ; Kinetics ; Male ; Membrane Potentials ; Myocytes, Cardiac ; metabolism ; Rabbits ; Sodium Channels ; physiology

Voltage-gated sodium (Nav) channels are indispensable membrane elements for the generation and propagation of electric signals in excitable cells. The successes in the crystallographic studies on prokaryotic Nav channels in recent years greatly promote the mechanistic investigation of these proteins and their eukaryotic counterparts. In this paper, we mainly review the progress in computational studies, especially the simulation studies, on these proteins in the past years.
Ion Channel Gating ; Ligands ; Models, Biological ; Permeability ; Substrate Specificity ; Voltage-Gated Sodium Channels ; chemistry ; metabolism

Voltage is an important parameter that regulates the conductance of both intercellular and plasma membrane channels (undocked hemichannels) formed by the 21 members of the mammalian connexin gene family. Connexin channels display two forms of voltage-dependence, rectification of ionic currents and voltage-dependent gating. Ionic rectification results either from asymmetries in the distribution of fixed charges due to heterotypic pairing of different hemichannels, or by channel block, arising from differences in the concentrations of divalent cations on opposite sides of the junctional plaque. This rectification likely underpins the electrical rectification observed in some electrical synapses. Both intercellular and undocked hemichannels also display two distinct forms of voltage-dependent gating, termed Vj (fast)-gating and loop (slow)-gating. This review summarizes our current understanding of the molecular determinants and mechanisms underlying these conformational changes derived from experimental, molecular-genetic, structural, and computational approaches.
Animals ; Connexins/chemistry/*metabolism ; Humans ; *Ion Channel Gating ; Ion Channels/chemistry/*metabolism ; Molecular Dynamics Simulation ; Protein Conformation

In the retina, pH fluctuations may play an important role in adapting retinal responses to different light intensities and are involved in the fine tuning of visual perception. Acidosis occurs in the subretinal space (SRS) under pathological conditions such as age-related macular degeneration (AMD). Although it is well known that many transporters in the retinal pigment epithelium (RPE) cells can maintain pH homeostasis efficiently, other receptors in RPE may also be involved in sensing acidosis, such as acid-sensing ion channels (ASICs). In this study, we investigated whether ASIC1a was expressed in the RPE cells and whether it was involved in the function of these cells. Real-time RT-PCR and Western blotting were used to analyze the ASIC1a expression in ARPE-19 cells during oxidative stress induced by hydrogen peroxide (H(2)O(2)). Furthermore, inhibition or over-expression of ASIC1a in RPE cells was obtained using inhibitors (amiloride and PCTx1) or by the transfection of cDNA encoding hASIC1a. Cell viability was determined by using the MTT assay. The real-time RT-PCR and Western blotting results showed that both the mRNA and protein of ASIC1a were expressed in RPE cells. Inhibition of ASICs by amiloride in normal RPE cells resulted in cell death, indicating that ASICs play an important physiological role in RPE cells. Furthermore, over-expression of ASIC1a in RPE cells prolonged cell survival under oxidative stress induced by H(2)O(2). In conclusion, ASIC1a is functionally expressed in RPE cells and may play an important role in the physiological function of RPE cells by protecting them from oxidative stress.
Acid Sensing Ion Channels ; metabolism ; Cell Line ; Humans ; Ion Channel Gating ; physiology ; Oxidative Stress ; physiology ; Retinal Pigment Epithelium ; cytology ; metabolism

The different concentration of specific ion species and the electrodiffusion of the ions down their electrochemical gradient generate transmembrane potential. The regulation of membrane potential for the function of numerous membrane proteins such as ion channels, transporters, pumps and enzymes plays primary role in the conversion of extracellular electric stimulation into a sequence of intracellular biochemical signals. Some ion channels regulated by membrane potential are well known, and the membrane non-ion channels protein is also modulated physiologically by membrane potential.
Humans ; Ion Channel Gating ; physiology ; Ion Channels ; metabolism ; Membrane Potentials ; physiology ; Phosphoric Monoester Hydrolases ; metabolism ; Receptors, G-Protein-Coupled ; metabolism

OBJECTIVETo investigate electrophysiology of cardiocytes in ligament of Marshall.

METHODSThe single cardiocytes obtained from ligament of Marshall were direct observed under inverted microscope. The cardiocyte action potential and current density of I(Na), I(Ca), L, I(to), I(K) and I(K1) were researched by whole-cell patch-clamp techniques.

RESULTSThere were two different cardiomyocytes in ligament of Marshall, one was rod shape, the other was short-rectangle shape. The short-rectangle myocyte was short and thick; the rod myocyte was long and thin. The short-rectangle myocyte was more than rod myocyte. The length/width rate of short-rectangle myocyte was less than that of rod myocyte (2.99 +/- 0.95 vs 12.05 +/- 2.41, P < 0.01). The action potential of ligament myocytes was similar to fast responsive cells. The action potential amplitude (APA) and duration (APD) of short-rectangle cells were less than those in rod cells. APA (mV), APD(50) (ms) and APD(90) (ms) were respectively 80.02 +/- 3.68 vs 91.72 +/- 7.56, 69.62 +/- 6.33 vs 83.14 +/- 3.66 and 107.55 +/- 4.25 vs 144.00 +/- 5.15, P < 0.05. The ion current density of I(Na), I(Ca), L, I(to), I(K1) was different between the two kind cells.

CONCLUSIONSThere are two different cardiocytes in ligament of Marshall. The action potential and ion current density of I(Na), I(Ca), L, I(to), I(K1) are different between the two kind cardiocytes.

Action Potentials ; Animals ; Dogs ; Electrophysiology ; Ion Channel Gating ; Ligaments, Articular ; metabolism ; Male ; Myocytes, Cardiac ; metabolism ; physiology ; Patch-Clamp Techniques

BACKGROUND AND OBJECTIVES: The endolymph produced from cochlear lateral wall regulates fluid and maintains positive endocochlear potential. Although many immunohistochemical studies of ion transport enzymes in the cochlear lateral wall have been reported, their mechanisms are still not completely understood. And there are no reports on the studies of anti-Na+ channels in the cochlea of the guinea pig. The voltage-dependent ion channels are fundamental components of neuronal activity. The Na+ channel has a single alpha subunit with 4 pseudosubunits of 6 transmembrane segments each. Expression of the pore-forming and voltage-sensing alpha or alpha1 subunit typically leads to the appearance of channels with voltage- and time-dependent gating and ion conductance. The purpose of this study is to evaluate the expression of the Na+ channel type I and II in the cochlea lateral wall. MATERIALS AND METHODS: We investigated the protein identification by western blot after homogenization and immunohistochemical localization by FITC to the anti-Na+ channel type I and II in the cochlea of the Preyer's positive, white guinea pigs. RESULTS: The results showed that the anti-Na+ channel type I and II were expressed strongly in the intermediate cells of the stria vascularis, and weakly in the stria vascularis. CONCLUSION: We suggest that there are voltage-dependent Na+ channels in the stria vascularis of cochlea and those functions are further evaulated physiologically by the patch clamp technique.
Animals ; Blotting, Western ; Cochlea* ; Endolymph ; Fluorescein-5-isothiocyanate ; Guinea Pigs* ; Guinea* ; Ion Channel Gating ; Ion Channels ; Ion Transport ; Neurons ; Stria Vascularis