Channels

Question 1

what are the sources of ion channel diversity?

Answer 1

structure, selectivity, conductance, gating, and kinetics

Question 2

what is x-ray crystallography used to visualize?

Answer 2

structure of ion channels such as the type of subunits present, pore region, and the presence of voltage sensors

Question 3

what causes ion channels to open and close?

Answer 3

depolarization (inside becomes less negative) causes them to open and repolarization (inside becomes more negative) causes them to close

Question 4

what are the different factors that influence ion channel structure?

Answer 4

trans-membrane spanning heteromeric/homomeric subunits, pore region, voltage sensor (positive or negative transmembrane loop that move with the membrane potential, opposite charge between voltage sensor and inside of the cell attract and close the pore and vice versa), auxiliary subunits modify how fast or slow a channel opens

Question 5

what are the different factors that influence ion channel selectivity?

Answer 5

pore size (will the ion be able to travel through pore with its water shell attached) and the selectivity filter (component of each subunit that contains charged amino acid residues that interact with ions and strip their water shell)

Question 6

what are the different factors that influence ion channel conductance?

Answer 6

whether the channel conducts ions or molecules, the direction of conductance, and modification of conductance by blockers, toxins, and drugs

Question 7

ohmic vs inward rectifying vs outward rectifying channels

Answer 7

ohmic: symmetrical, ions can pass in either direction
inward rectifying: asymmetrical, ions flow in
outward rectifying: asymmetrical, ions flow out

Question 8

what are the types of blockers, toxins and drugs that can modify conductance?

Answer 8

blockers: Mg+ blocks Ca2+ from passing through the NMDAR
toxins: tetrodotoxin blocks sodium channels
drugs: norvasc blocks calcium channels

Question 9

heteromeric vs homomeric subunits

Answer 9

heteromeric: at least one different subunit
homomeric: 4 identical subunits

Question 10

what are the three gating states of ion channels?

Answer 10

resting: closed but able to be activated
open: active, all or none
refractory: closed but not able to be activated

Question 11

desensitization vs inactivation

Answer 11

desensitization: the state in which an ion channel becomes refractory due to prolonged ligand exposure
inactivation: channel cannot open because it needs to undergo a change

Question 12

what are the different types of ion channels that have gating that is determined by a stimuli?

Answer 12

voltage gated, ligand gated, signal gated, thermosensitive, mechanosensitive

Question 13

what are the different types of ion channels that’s gating is not determined by a stimuli?

Answer 13

open/leak channels, aquaporin, and connexon

Question 14

what kind of stimuli influences the gating of voltage gated channels?

Answer 14

effects K+, Na+, Ca2+, Cl- channels, opposite attraction between channel and ion opens gate

Question 15

what kind of stimuli influences the gating of ligand gated channels?

Answer 15

effects GABAR, AMPAR, and NMDAR, extracellular neurotransmitters bind to channel which allows them to open

Question 16

what kind of stimuli influences the gating of signal gated channels?

Answer 16

effects cAMP, Ca2+, P, H+, and GTP, intracellular or extracellular neurotransmitters bind to the channel which allows them open, often responsive to changes in pH (changes in H+ concentration, high H+ = high pH)

Question 17

what kind of stimuli influences the gating of thermosensitive channels?

Answer 17

transient receptor potential (TRP) channels sense pain and temperature, temperature rearranges the subunits forming the channel to allow it to open and send signal

Question 18

what kind of stimuli influences the gating of mechanosensitive channels?

Answer 18

transient receptor potential (TRP) channels open in response to pressure

Question 19

how do open/leak, aquaporin, and connexon channels work?

Answer 19

open/leak: make up certain K+, Na+, and Cl- channels in neurons, stay open most of the time
aquaporin: regulate how much water enters cell
connexon: quaternary protein structure that connects adjacent cells

Question 20

what are the different types of K+ channels?

Answer 20

KV2.1 channels, KV4.2 channels, inward rectifier K+ channels, 2P K+ channels, and Ca2+ activated K+ channels

Question 21

what are KV2.1 channels?

Answer 21

voltage gated, rapid opening, slow inactivation, gates excitation in dendrites (meaning there is a refractory period), role in repolarization

Question 22

what are KV4.2 channels?

Answer 22

voltage gated, rapid inactivation, responsive to depolarization

Question 23

what are inward rectifier K+ channels?

Answer 23

voltage gated but allow peak current through during hyperpolarization

Question 24

what are 2P K+ channels?

Answer 24

2 subunits make up poor region, voltage-independent, signal gated (responsive to changes in pH, H+), leak channels allow H+ to escape to maintain membrane potential

Question 25

what are Ca2+ activated K+ channels?

Answer 25

signal gated by intracellular Ca2+ (lets Ca2+ out), open when cell is more hyperpolarized and membrane potential is lower

Question 26

what are HCN channels?

Answer 26

voltage-gated, hyperpolarization activated cation (+) channels, support depolarization/spontaneous firing, any cation can pass, cell is not as negative at rest so it hovers closer to the threshold

Question 27

what are the two types of active transporters?

Answer 27

ATPase pumps and ion exchangers

Question 28

what do sodium-potassium-ATPase pumps do?

Answer 28

pumps 2 K+ and 3 Na+ ions against their concentration gradients (Na+ out, K+ in) using ATP, responsible for 2/3 of the total energy consumption of the brain

Question 29

how does ATP supply energy?

Answer 29

ATP is dephosphorylated to become ADP which releases a phosphate and energy from the broken bond

Question 30

what are the three types of ion exchangers?

Answer 30

Na+/Ca2+ antiporter, Na+/H+ antiporter, and Cl- Co-transporters (symporters)

Question 31

what do Na+/Ca2+ antiporters do?

Answer 31

use electrochemical energy that is freed up by transporting Na+ along its electrostatic gradient (into the cell) to move Ca2+ against its gradient (out of the cell), regulates intracellular Ca2+

Question 32

what do Na+/H+ antiporters do?

Answer 32

use energy freed from transporting Na+ along its electrostatic gradient (into the cell), to move H+ against its gradient (out of the cell), regulates intracellular pH (deacidifies the cell by removing H+)

Question 33

what do Cl- co-transporters (symporters) do?

Answer 33

Na+ - K+ - 2Cl cotransporter 1 (NKCC1) moves K+, 2Cl-, and Na+ into the cell, K+ - Cl- cotransporter 2 (KCC2) moves K+ and Cl- out of the cell

Question 34

how does the amount of Cl- within a cell change throughout time?

Answer 34

in early development GABAR transporters pump the high Cl- out of the cell, this depolarizes the cell bringing it closer threshold making GABA excitatory, in adulthood there is much less Cl- in the cell so GABAR now act to pump Cl- into the cell, this hyperpolarizes the cell bringing it farther from threshold making GABA inhibitory

Question 35

how is epilepsy effected by Cl- co-transporters?

Answer 35

epilepsy causes a reversion to NKCC1 which means that GABAR receptors pump Cl- out of the cell, making it excitatory and brining cells closer to threshold

Question 36

efflux vs influx

Answer 36

efflux: ions move out of the cell
influx: ions move into the cell