Sweetening K-channels: what sugar taught us about permeation and gating.

Because they enable for the modification of both viscosity and osmolarity, sugars have been used as a biophysical probe of voltage-gated K-channels for a while. Viscosity variations made it possible to measure the pore sizes in large and small conductance K-channels using techniques similar to those used in the 1980s to study the gramicidin A channel. These analyses led to the finding that the size of the internal mouth appears to be the primary cause of the conductance differences between Shaker-like channels and large conductance BK-channels.

A scenario for the origin of life: Volume regulation by bacteriorhodopsin required extremely voltage sensitive Na-channels and very selective K-channels.

The osmotic activity produced by internal, non-permeable, anionic nucleic acids and metabolites causes a persistent and life-threatening cell swelling, or cellular edema, produced by the Gibbs-Donnan effect. This evolutionary-critical osmotic challenge must have been resolved by LUCA or its ancestors, but we lack a cell-physiology look into the biophysical constraints to the solutions. Like mycoplasma, early cells conceivably preserved their volume with Cl , Na , and K -channels, Na /H -exchangers, and a light-dependent bacteriorhodopsin-like H -pump.

Which Are the Commonest Sites and Characteristics of Post-Transurethral Prostate Surgery Strictures in a High-Volume Reconstructive Center?

Urethral stricture is a well-known complication after transurethral prostate surgery (TPS) and it is usually considered an easy-to-treat condition. We aimed to examine characteristics of post-TPS urethral stricture cases that were referred for urethroplasty at our tertiary center. We identified 201 patients with TPS-induced stricture treated with urethroplasty at our institution from 2017 to 2021.

Neural Network Model for Predicting Student Failure in the Academic Leveling Course of Escuela Politécnica Nacional.

The purpose of this study is to train an artificial neural network model for predicting student failure in the academic leveling course of the Escuela Politécnica Nacional of Ecuador, based on academic and socioeconomic information. For this, 1308 higher education students participated, 69.0% of whom failed the academic leveling course; besides, 93.

Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic Strength.

κ-Conotoxin-PVIIA (κ-PVIIA) is a potassium-channel blocking peptide from the venom of the fish-hunting snail, , which is essential for quick prey's excitotoxic immobilization. Binding of one κ-PVIIA to K-channels occludes the K-conduction pore without additional conformational effects. Because this 27-residue toxin is +4-charged at neutral pH, we asked if electrostatic interactions play a role in binding.

Trans-toxin ion-sensitivity of charybdotoxin-blocked potassium-channels reveals unbinding transitional states.

In silico and in vitro studies have made progress in understanding protein-protein complex formation; however, the molecular mechanisms for their dissociation are unclear. Protein-protein complexes, lasting from microseconds to years, often involve induced-fit, challenging computational or kinetic analysis. Charybdotoxin (CTX), a peptide from the scorpion venom, blocks voltage-gated K-channels in a unique example of binding/unbinding simplicity.

Gating-induced large aqueous volumetric remodeling and aspartate tolerance in the voltage sensor domain of Shaker K channels.

Neurons encode electrical signals with critically tuned voltage-gated ion channels and enzymes. Dedicated voltage sensor domains (VSDs) in these membrane proteins activate coordinately with an unresolved structural change. Such change conveys the transmembrane translocation of four positively charged arginine side chains, the voltage-sensing residues (VSRs; R1-R4).

Pore size matters for potassium channel conductance.

Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K(+) channels discriminate K(+) over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K(+) channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings.

Effective pore size and radius of capture for K(+) ions in K-channels.

Reconciling protein functional data with crystal structure is arduous because rare conformations or crystallization artifacts occur. Here we present a tool to validate the dimensions of open pore structures of potassium-selective ion channels. We used freely available algorithms to calculate the molecular contour of the pore to determine the effective internal pore radius (r(E)) in several K-channel crystal structures.

Zebrafish CaV2.1 calcium channels are tailored for fast synchronous neuromuscular transmission.

The CaV2.2 (N-type) and CaV2.1 (P/Q-type) voltage-dependent calcium channels are prevalent throughout the nervous system where they mediate synaptic transmission, but the basis for the selective presence at individual synapses still remains an open question.

K(+) channels: function-structural overview.

Potassium channels are particularly important in determining the shape and duration of the action potential, controlling the membrane potential, modulating hormone secretion, epithelial function and, in the case of those K(+) channels activated by Ca(2+), damping excitatory signals. The multiplicity of roles played by K(+) channels is only possible to their mammoth diversity that includes at present 70 K(+) channels encoding genes in mammals. Today, thanks to the use of cloning, mutagenesis, and the more recent structural studies using x-ray crystallography, we are in a unique position to understand the origins of the enormous diversity of this superfamily of ion channels, the roles they play in different cell types, and the relations that exist between structure and function.

K⁺ conduction and Mg²⁺ blockade in a shaker Kv-channel single point mutant with an unusually high conductance.

Potassium channels exhibit a large diversity of single-channel conductances. Shaker is a low-conductance K-channel in which Pro475→Asp, a single-point mutation near the internal pore entrance, promotes 6- to 8-fold higher unitary current. To assess the mechanism for this higher conductance, we measured Shaker-P475D single-channel current in a wide range of symmetrical K(+) concentrations and voltages.

Hypothyroidism in the adult rat causes incremental changes in brain-derived neurotrophic factor, neuronal and astrocyte apoptosis, gliosis, and deterioration of postsynaptic density.

Background: Adult hypothyroidism is a highly prevalent condition that impairs processes, such as learning and memory. Even though tetra-iodothyronine (T(4)) treatment can overcome the hypothyroidism in the majority of cases, it cannot fully recover the patient's learning capacity and memory. In this work, we analyzed the cellular and molecular changes in the adult brain occurring with the development of experimental hypothyroidism.

Reduced voltage sensitivity in a K+-channel voltage sensor by electric field remodeling.

Propagation of the nerve impulse relies on the extreme voltage sensitivity of Na(+) and K(+) channels. The transmembrane movement of four arginine residues, located at the fourth transmembrane segment (S4), in each of their four voltage-sensing domains is mostly responsible for the translocation of 12 to 13 e(o) across the transmembrane electric field. Inserting additional positively charged residues between the voltage-sensing arginines in S4 would, in principle, increase voltage sensitivity.

Slow inactivation in Shaker K channels is delayed by intracellular tetraethylammonium.

After removal of the fast N-type inactivation gate, voltage-sensitive Shaker (Shaker IR) K channels are still able to inactivate, albeit slowly, upon sustained depolarization. The classical mechanism proposed for the slow inactivation observed in cell-free membrane patches--the so called C inactivation--is a constriction of the external mouth of the channel pore that prevents K(+) ion conduction. This constriction is antagonized by the external application of the pore blocker tetraethylammonium (TEA).

Mutations of nonconserved residues within the calcium channel alpha1-interaction domain inhibit beta-subunit potentiation.

Voltage-dependent calcium channels consist of a pore-forming subunit (Ca(V)alpha(1)) that includes all the molecular determinants of a voltage-gated channel, and several accessory subunits. The ancillary beta-subunit (Ca(V)beta) is a potent activator of voltage-dependent calcium channels, but the mechanisms and structural bases of this regulation remain elusive. Ca(V)beta binds reversibly to a conserved consensus sequence in Ca(V)alpha(1), the alpha(1)-interaction domain (AID), which forms an alpha-helix when complexed with Ca(V)beta.

Calcium channel subtypes differentially regulate fusion pore stability and expansion.

Various studies have focused in the relative contribution of different voltage-activated Ca(2+) channels (VACC) to total transmitter release. However, how Ca(2+) entry through a given VACC subtype defines the pattern of individual exocytotic events remains unknown. To address this question, we have used amperometry in bovine chromaffin cells.

Slow inactivation in voltage gated potassium channels is insensitive to the binding of pore occluding peptide toxins.

Voltage gated potassium channels open and inactivate in response to changes of the voltage across the membrane. After removal of the fast N-type inactivation, voltage gated Shaker K-channels (Shaker-IR) are still able to inactivate through a poorly understood closure of the ion conduction pore. This, usually slower, inactivation shares with binding of pore occluding peptide toxin two important features: i), both are sensitive to the occupancy of the pore by permeant ions or tetraethylammonium, and ii), both are critically affected by point mutations in the external vestibule.

Inhibition of single Shaker K channels by kappa-conotoxin-PVIIA.

kappa-Conotoxin-PVIIA (kappa-PVIIA) is a 27-residue basic (+4) peptide from the venom of the predator snail Conus purpurascens. A single kappa-PVIIA molecule interrupts ion conduction by binding to the external mouth of Shaker K channels. The blockade of Shaker by kappa-PVIIA was studied at the single channel level in membrane patches from Xenopus oocytes.

Splitting the two pore domains from TOK1 results in two cationic channels with novel functional properties.

Potassium channels are membrane-spanning proteins with several transmembrane segments and a single pore region where ion conduction takes place (Biggin, P. C., Roosild, T.