Lecture 6 Flashcards
Channels that conduct Na+ have what effect on the cell?
Depolarization
Channels that conduct K+ have what effect on the cell?
Hyperpolarization
Channels that conduct Ca2+ have what effect on the cell?
Depolarization (Ca2+ signalling)
Channels that conduct Cl- have what effect on the cell?
Depolarization or hyperpolarization, depending on gradient
Where are nicotinic acetylcholine receptors expressed?
Vertebrate neuron-muscle synapses (neuromuscular junctions), vertebrate and invertebrate neurons
What are the classical modecular techniques for characterizing ion channels and receptors? (4)
- Biochemically isolate and identify the channel protein and its subunits
- Determine the channel’s protein and mRNA sequences
- Clone the channel coding sequence and use that to express the channel in cells for electrophysiological characterization
- Make mutations in the channel coding sequence to test hypotheses about how specific amino acids might contribute to its function
What was used to purify nACh receptors from Torpedo cell lysates?
alpha-bungarotoxin
How many subunits make up an nACh receptor?
5
How many transmembrane helices are in an nACh receptor?
4
What are transmembrance helices made up of?
Hydrophobic amino acids
What is characteristic of cys-loop channels? (2)
5 subunits, 4 transmembrane helices
Extracellular loop formed by disulphide bond between 2 cysteine amino acids
Are GABA receptors anionic or cationic?
Anionic
Are glycine receptors anionic or cationic?
Anionic
Are serotonin receptors anionic or cationic?
Cationic
Are MOD-1 (serotonin) receptors anionic or cationic?
Anionic
Are glutamate-gated receptors anionic or cationic?
Anionic
Are EXP-1 (GABA) receptors anionic or cationic?
Cationic
What are cys-loop receptors also referred to as? (2)
Ionotropic receptors
Ligand-gated channels
What are cholinergic neurons?
Neurons that secrete acetylcholine
What are serotonergic neurons?
Neurons that secrete serotonin
What are GABAergic neurons?
Neurons that secrete GABA
What are glycinergic neurons?
Neurons that secrete glycine
What is x-ray crystallography?
Make crystal of protein, use x-ray diffraction (like a projector slide) to infer protein stucture
What is cryo-electron microscopy?
Cryogenically freeze sample and image with electron beam
What makes up a selectivity filter in pore-loop channels?
4 P-loops which project amino acids into pore
What is a K_IR protein?
Inward rectifying potassium channel
Tandem duplication of a K_IR protein resulted in…
2-pore K+ channels
Inversion and addition of a TMH to K_IR protein resulted in…
Ionotropic glutamate receptors
What is an HCN channel?
Hyperpolarization-activated cyclic nucleotide-gated channel (activated by hyperpolarization, cAMP, and cGMP)
What is a TRP channel?
Transient receptor potential channel (activated by light, chemicals, osmotic pressure, temperature)
What is a small conductance K+ channel (SK)?
Ca2+ or depolarization activated K+ channel with a calcium sensor at C-terminus
What is a big conductance K+ channel (BK)?
Ca2+ or depolarization activated K+ channel that directly binds calcium at C-terminus
What are Na_V channels?
Voltage gated Na channels
What are Ca_V channels?
Voltage gated K channels
What are NALCN channels?
Non-selective leak channels
Addition of a voltage sensor to K_IR resulted in…
Voltage gated channels
Addition of Ca2+ sensitive modules to K_IR resulted in…
SK and BK channels
Duplication of a 2-pore channel resulted in…
4-domain channels
How do K_IR channels select for K+?
Carbonyl oxygens projected from P-loops into pore which minic hydration shell oxygens surrounding K+ in solution
What are two selectivity filter motifs in Ca_V channels?
EEEE and EEDD
What is the selectivity filter motif in Na_V channels in humans?
DEKA
What are two selectivity filter motifs in Na_V channels in earlier invertebrates?
DKEA and DEEA
Describe the sliding helix model
At rest, S4 helix repelled into membrane by extracellular cations and attracted into membrane by intracellular anions (closed channel)
Upon depolarization, S4 helix slides through membrane and creates an outward ‘cation current’
Describe N-type inactivation
“Ball and chain model”, cytoplasmic N-terminal structure moves in to plug pore. Fast.
Describe C-type inactivation
Conformatinal changes through channel structure close pore. Slow.
How many connexins/pannexins/innexins make up a hemi-channel?
6
Which of the following can form gap junctions? Connexins, innexins, pannexins
Connexins and innexins
What induces hemi-channel opening?
Membrane depolarization
What are hemi-channels permable to?
ATP outward
Dyes inward
What are the functions of gap-junctions? (2)
- Mediate electrical coupling between cells
2. Permit sharing of resources (soluble membrane impermeable molecules)
What are the functions of hemi-channels? (2)
- Mediate release of signaling molecules such as ATP and glutamate
- Activate ATP-gated cation channels (Purinergic receptors) for cell-cell (paracrine) and self (autocrine) signaling
