Sodium Channels and Nonselective Cation Channels An Introduction
- Slides: 36
Sodium Channels and Nonselective Cation Channels An Introduction Corthell, 2007
Outline w Sodium Channels w Types w Regulatory mechanisms (a few) w Pharmacology (and what it shows us) w Structure w Paper-”Role of hydrophobic residues…” w Nonselective Cation Channels w Where they are w What they are w TRP channels-well-characterized w Paper-”TRPC 3 Channels Are Necessary…”
Sodium (Na) Channel Types w Voltage-gated Na Channels w Include ‘voltage sensor’ on protein w Crucial to establish an action potential (AP) w Found in various systems with variant effects and ‘operating voltages’ w Ligand-gated Na Channels w Bind to specific ligand generate electrical response
Voltage-Gated http: //www. mun. ca/biology/desmid/brian/BIOL 2060 -13/1309. jpg
Ligand-Gated http: //www. mun. ca/biology/desmid/brian/BIOL 2060 -13/1323. jpg
Regulation and Modulation in Na Channels w Phosphorylation w NO modulates Na effects currents (Ribeiro et al. , 2007) w Mutations in ball-and w NO donors reduce -chain affect peak Na current inactivation speed w Cleavage of any part w ENa. C modulated by accessory proteins of Na channel (Gormley et al. , protein 2003) w Drugs can be used as modulators
Pharmacology (i. e. drugs of choice) w Saxitoxin (STX), from red tide, used to count Na channels (Ritchie et al. 1976) w Tetrodotoxin (TTX), from fugu puffer fish, local anesthetics also block Na channel flux w Local anesthetic: # channels open at once Saxitoxin www. chemfinder. com
w Drugs bind to receptors w Can be used to count receptors, block channels (ex: identify which current is responsible for some spiking) w Na channel is not perfectly selective w Also permeable to K+ ions, though much less than Na+ (Chandler and Meves, 1965) w Therefore, drug application may not necessarily block one ion completely w Drug responses are variable w Cardiac cells respond less to TTX than skeletal muscle cells (Ritchie and Rogart, 1977; Cohen et al. , 1981)
Structural Drug Use w TTX and STX used to w Other drugs used to identify Na channel identify other proteins (Henderson channel proteins as and Wang, 1972) well as their receptor sites w Irradiated TTX and STX used as markers for bound portions of protein
Na Channel Structure w 6 transmembrane domains (S 1 -S 6) w 4 repeats (Domain 1 -4) w Has , , and subunits w subunit responsible for pore w P-loop as selectivity filter
w Single linked protein makes up ion channel w P-loop reflects speed of inactivation w , subunits modify channel function but are not essential to create the pore w Ligand-gated channels do not have voltage sensor, but ligand binding site w Voltage gated channels have voltage sensor on S 4 in each domain w Speculation: domain sensors have special functions (Kuhn and Greef, 1999)
Epithelial Na Channel (ENa. C)
ENa. C in kidney, colon, and lungs w Kidney: ENa. C aids in Na. Cl reabsorption w Maintains body Na. Cl balance and blood pressure (Garty and Benos, 1988) w Lungs: aids in fluid clearance from alveolar space w Maintains normal gas exchange in lungs (Matalon and O’Brodovich, 1999) w Affected by aldosterone and vasopressin w Alter rate of insertion, degradation, recycling of channels w Helped identify channel recycling by clathrinmediated endocytosis (Shimkets et al. , 1997)
Nicotinic Acetylcholine Receptor (n. Ach. R) Model of the ligandbinding domain Mature muscle expresses different subunits than fetal muscle http: //s 12 ap 550. biop. ox. ac. uk: 8078/dynamite_html/gallery_files/n. ACh. R_covariance_lines_small. p ng
Paper: “Role of hydrophobic residues in the voltage sensors of the voltage-gated sodium channel” Bendahhou et al. , 2007) w S 4 of each domain is considered the voltage sensor w Major players include Arg and Lys residues occurring every 3 a. a. s and separated by 2 neutral residues w Mutate nonpolar Phe and Leu to Ala w Eliminate steric hindrance w Follow up with patchclamp recording Alter D 1 -D 3, as D 4 S 4 has been studied extensively
w D 1 and D 2 voltage sensor mutations did not result in significantly altered activation/inactivation kinetics…
w …but did alter the activation curve. L 224 A is shifted to a hyperpolarized voltage, enhancing the open state, while L 227 A is shifted to a depolarized voltage (favors closed)
w D 3 mutations led to altered fast inactivation and a voltage shift in inactivation to hyperpolarization
Paper Summary w Hydrophobic residues are also important to the voltage sensor w Need correct shape w Altering the voltage sensor on D 1 and D 2 alters inactivation/activation kinetics w Mutations on D 3 S 4 alter kinetics and voltage dependence w Leads to idea: perhaps each S 4 responsible for different aspects of channel gating? Do they function independently?
Nonselective Cation Channels w Where? w Across most sensory systems as transduction channels w Examples: retinal rods, hair cells, Pacinian corpuscle, spindle organs, taste cells (amino acid taste), nociception w TRP channels extensively studied w Broad family of nonselective cation channels w In brain, aiding in spontaneous firing (Kim et al. , 2007)
Stretch Receptors www. unm. edu/~toolson/ pacinian_corpuscle. gif
What are nonselective cation channels? w Obvious answer… w Not necessarily a ‘universal’ structure w However, most NCCs like Na or K channels are known for w Depends on fluxing Ca 2+ w Mostly due to chemical gradient of Ca outside of cell w Still flux Na+, K+ sequence homology, location of channel
Transient Receptor Potential (TRP) Channels w Very large gene family-many divisions w TRPM, TRPC, TRPV… w Widely expressed in brain (including hippocampus) w Structural similarity, but still many differences between channel structures and functions
Structure w TRP channels have 6 transmembrane segments (similar to Kv channels) w Between S 5 and S 6 is believed to be pore w TRP domain: highly conserved 25 a. a. s C-terminal to S 6 w Include 6 invariant a. a. s , called TRP box w Different subunits: made up of homoand heterotetramers w Ankyrin repeats (33 a. a. s) crucial for some subunits to assemble
TRPC 3 structure (proposed) Mio et al. , 2007
w TRP channels are w Many of these known to have many channels are also different ligands activated by Ca 2+ (capsaicin-TRP binding (Amaral and relative VR 1 [Cesare Pozzo-Miller, 2007) and Mc. Naughton, 1996, 1997], PIP 2 TRPV [Nilius et al. , 2007])
Paper-”TRPC 3 Channels Are Necessary for Brain-Derived Neurotrophic Factor to Activate a Nonselective Cationic Current and to Induce Dendritic Spine Formation” Amaral and Pozzo-Miller, 2007. w BDNF elicits a current that is not blocked by tetrodotoxin or saxitoxin but is blocked by interfering RNA-mediated knockdown of TRPC 3 w BDNF application also increases surface TRPC 3 in cultured hippocampal neurons
w Long-term BDNF exposure leads to various effects on hippocampal neurons w Can modulate synaptic transmission w Can change structure of dendrites, spines, and presynaptic terminals w Kept in serum-free media to avoid effects of serum nutrients w Slowly activating, sustained current w Different than other Trk receptor cation fluxes
w In voltage clamp. K-252 a is a tyrosine kinase inhibitor, showing that the BDNF response requires one
w Current is not blocked by saxitoxin w TRPC currents expressed in hippocampal neurons
w BDNF application alters amount of TRPC 3 on surface
w Spines affected by different drugs, including TRPC inhibitors w Spines counted
Paper Summary w BDNF increases density of dendritic spines on hippocampal neurons (CA 1) w Works via a TRPC 3 conductance w Uses Trk. B receptors, phospholipase C, others w Therefore, TRPC 3 channels are mediators of BDNFmediated dendritic remodeling
Summation w Na channels have multiple locations, uses, responses w Well-studied w Structure still not elucidated w Isoforms part of historical work w Nonselective cation channels are found in most sensory systems w Transduction channels or TRP channels w Many different purposes, depending on host cell
- Is acebutolol selective or nonselective
- Sodium carbonate reacts with hydrochloric acid
- Redox volumetric analysis
- Balance the following chemical equations
- Oxygen bleach vs chlorine bleach
- What is the iupac name of the base naoh?
- Honh2 dissociation equation
- Tin iv sulfate formula
- Fe 3+ + br-
- Limiting radius ratio
- Mass of kclo3
- Hbr cation and anion
- Calcium iodide cation and anion
- Ligação ionica
- Cation exchange capacity
- Saneamento
- Radio de los atomos
- Different ions
- Polyatomic cation
- Como se forman los iones
- Types of ions
- Cation exchange chromatography
- Positive ions and negative ions table
- Configuracion electronica de un cation divalente
- The proper chemical formula for auric nitride is
- Cation trivalente
- Cycloheptatrienyl cation
- Acidic salts examples
- Cation joke
- Cicloheptatrienilo
- Benzenoid and non benzenoid
- Project copenheimer
- Pentadienyl anion molecular orbitals
- Cation
- Neon cation or anion
- Eso
- Elution order