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#ion channels

13 public questions tagged with this topic.

Fertilization in mammals-l

Sperm-specific calcium channel in hyperactivation:

Hyperactivation, characterized by high-amplitude asymmetric flagellar beating generating enhanced thrust for cumulus and zona penetration, depends absolutely on calcium entry through CatSper, sperm-specific voltage and pH sensitive calcium channel complex localized to principal piece flagellum. Subunits CatSper1-4 plus auxiliary proteins form heteromeric pore gated by intracellular alkalinization and progesterone removing endocannabinoid inhibition. Calcium influx activates calmodulin, altering dynein sliding pattern. CatSper knockout males are infertile despite normal counts, sperm unable to

Ref: Ren et al., Nature 2001: CatSper calcium channel required for hyperactivation and male fertility in mammals.

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Fertilization in mammals-ll

Sperm hyperactivation is mediated by opening of:

Hyperactivation is vigorous, high-amplitude asymmetric flagellar beating pattern required for penetrating cumulus matrix and zona pellucida. Transition from progressive motility depends on massive calcium influx through sperm-specific CatSper complex located in principal piece of flagellum. Progesterone from cumulus and intracellular alkalinization during capacitation activate CatSper, raising flagellar calcium, stimulating calmodulin kinases and altering dynein motor regulation. Resultant whip-like thrust generates increased force, and pharmacologic CatSper blockade prevents hyperactivation d

Ref: NCBI Bookshelf, Molecular Biology of the Cell, Chapter 15: CatSper and calcium-dependent hyperactivated motility mechanisms.

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Membrane Transportation

Which of the following statements about ionophores is false?

Ionophores are small hydrophobic organic molecules, typically cyclic peptides, depsipeptides or polyethers, produced by various soil microbes as competitors for niche colonization. Their defining functional attribute is capacity to overcome the high dielectric barrier of lipid bilayers for charged ions by providing a polar binding site shielded by hydrophobic exterior that readily partitions into membrane. By facilitating passive equilibration of ions down existing electrochemical gradients, they dissipate membrane potential, pH gradients and ion asymmetries, uncoupling oxidative phosphorylati

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 11: Ionophores as Mobile Carriers and Channel Formers.

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Membrane Transportation

Which segment of a voltage-gated ion channel detects changes in membrane potential?

Ion channel gating requires conversion of electrical signal into conformational change, accomplished by specialized sensor modules. Voltage-gated channels share a conserved architecture of four domains each comprising six membrane helices. S1, S2 and S3 are largely hydrophobic with interspersed acidic residues forming a charge transfer center and hydrophilic vestibules enabling helix motion. S4 stands out because it contains four to seven positively charged arginine or lysine residues spaced every third position in motif Arg-X-X-Arg, creating a linear array of gating charges along one face of

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter: Voltage-Sensing Domain S4 Movement and Gating Currents.

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Membrane Transportation

The selectivity filter in a voltage-gated sodium channel is formed by:

Selectivity in voltage-gated sodium channels arises from the narrowest region of the pore called the selectivity filter, located within the pore-forming domain. Each of the four homologous domains contributes S5 and S6 helices that line the central cavity, while the polypeptide linking S5 to S6 folds back into the membrane as a re-entrant loop. This loop contains two pore helices P1 and P2 flanking the filter. Residues from each domain project into the lumen forming rings: the outer EEDD ring of negatively charged glutamate and aspartate attracts cations, and the inner DEKA locus with aspartat

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 11: Structure of Voltage-Gated Sodium Channel Selectivity Filter DEKA Motif.

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Membrane Transportation

Which of the following is a voltage-gated sodium channel subunit responsible for sensing membrane potential?

Voltage-gated sodium channels that drive rapid upstroke of action potentials are built from one polypeptide folded into four homologous repeats, each repeat having six transmembrane helices S1 to S6. S1 through S4 cluster peripherally as the voltage-sensing domain, while S5, S6 and the intervening loop dip back into the membrane as P-loop to create the ion conducting pore. The hallmark of voltage sensing resides in S4, which exhibits a repeating pattern Arg-X-X where positively charged arginine or lysine appears every third residue, flanked by hydrophobic side chains. These gating charges sit

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 11: Voltage-Gated Ion Channels and Electrical Properties of Membranes.

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Membrane Transportation

Which of the following is a mechanically gated ion channel?

Mechanically gated ion channels convert physical deformation stretch pressure into electrical signals essential for touch hearing proprioception vascular tone and volume control. Stretch-activated cation channels in dorsal root sensory neurons including Piezo1 and Piezo2 giant proteins over thirty transmembrane helices propeller blades and TRP members like TRPV4 contain large curved domains acting as membrane tension sensors coupled to central pore. Increased lateral tension or cytoskeletal pulling flattens protein expanding fenestrations opening pore permeable to Na+ K+ Ca2+ generating recept

Ref: Ranade et al., Nature 2015: Piezo Proteins as Mechanically-Gated Stretch Channels.

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Membrane Transportation

A ligand-gated ion channel opens when:

Ligand-gated ion channels, also called ionotropic receptors, provide fastest chemical to electrical transduction at synapses through direct conformational coupling between binding and pore opening without second messengers. They are multimeric membrane proteins typically pentameric Cys-loop family including nicotinic acetylcholine, GABA-A, glycine and 5-HT3 receptors, or tetrameric glutamate receptors AMPA, NMDA and kainate, each with extracellular ligand-binding domain formed by loops and transmembrane pore domain of four helices M1-M4 surrounding central ion pathway. Binding of specific agon

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 15: Ligand-Gated Ion Channels – Mechanism.

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Membrane Transportation

Which of the following is a voltage-gated ion channel?

Gating mechanisms classify ion channels by physiological stimulus that controls transition from closed to open conformation. Voltage-gated channels possess specialized voltage-sensing domains where transmembrane segment S4 contains repeating positively charged arginine or lysine residues every third position, acting as sliding helix that moves outward upon membrane depolarization, pulling on S4-S5 linker and opening activation gate at intracellular bundle crossing. Neuronal voltage-gated sodium channels, Nav1.1 to Nav1.9 encoded by SCN genes, contain four homologous domains each with six helic

Ref: Hille, Ion Channels of Excitable Membranes, 3rd ed., Chapter 5: Voltage-Gated Sodium Channels in Neurons.

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Electrophysiological methods

Which method allows studying ligand-gated ion channels?

Ligand-gated ion channels such as nicotinic acetylcholine, GABA-A, glycine and ionotropic glutamate receptors open upon neurotransmitter binding, producing rapid postsynaptic currents. Studying them requires ability to apply agonist at defined concentrations while monitoring transmembrane current. Patch-clamp in outside-out or whole-cell mode permits rapid solution exchange via perfusion systems, recording dose-dependent activation, desensitization, single-channel conductance and allosteric modulation with pharmacological precision. EEG records summed population potentials, CT images anatomy u

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Electrophysiological methods

Which ion channel activity is best visualized using patch-clamp?

Observing stochastic opening and closing of an individual channel requires isolating its picoampere current from background of thousands of other channels. Patch-clamp achieves this by sealing a glass pipette against membrane with gigaohm resistance, confining one channel within patch. Cell-attached or excised patch modes reveal unitary amplitude, conductance states, burst behavior and pharmacological block of sodium, potassium, calcium and acetylcholine receptor channels. Simultaneous multi-channel macroscopic currents represent average activity, voltage-gated pumps transport actively without

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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