Channels and Transporters

Question 1

intro

Answer 1

• N and K currents change with increasing depol
• pos 52 early Na absent
• pos 65 early Na reverses
• outward K increases in mag as voltage goes more pos

Question 2

patch clamp

Answer 2

• suction to form a patch
• take it or leave it and break membrane
• provided evidence for single channel
• macroscopic manu channels

Question 3

patch clamp 2

Answer 3

• detects currents flowing through single membrane channels due to depolarization
• channels open/close all or none
• fast switch
• stochastic
• transition is gating-conformational change
• deopolarization increases probability that Na channel will open
• macroscopic current is aggregate of 1000s of microscopic currents
• stimulating patch increases prob of channel open
• K+ have delay and opposite direction

Question 4

Na channels

Answer 4

• voltage dependent
• open near beginning of depolarization
• inactivate
• current reverses Ena
• TTX blocks

Question 5

K channels

Answer 5

• voltage dependent
• open later
• just close
• TEA or Cs+ block
• multiple genes so channel can differ in activation, gating, inactivation
• shape complex electrical responses influence duration of AP and resting membrane potential

Question 6

multiple K channels

Answer 6

• add diversity
• most CNS neurons have multiple K channels with different characteristics
• voltage dependence of activation
• rate of activation
• inactivation properties-diversity of spike waveforms and patterns

Question 7

fast after hyperpol

Answer 7

• shortens AP
• repol quick
• only affects early spike freq at very high freq
• BK K channels
• activated by Ca depolarization
• rapid inactivation

Question 8

medium AHP

Answer 8

• controls early interspike interval
• contributes to early spike frequency adaptation
• slowly activating by Ca entry
• controls late spike frequency adaptation
• IK and SK channels
• don’t inactivate

Question 9

slow AHP

Answer 9

• limits firing freq

- unknown channel

Question 10

Ca channels

Answer 10

-in some neurons result in bursts of AP that may last 100 ms or longer

Question 11

voltage gated

Answer 11

-selectively permeable to one ion

Question 12

ligand gated

Answer 12

• respond to chemical signals

- can let in more than one ion

Question 13

Kv4.1

Answer 13

tumorigenic in mammary cells

-inactivate rapidly

Question 14

channel diversity

Answer 14

• mechanosensitive-touch, hearing, osmoreg, neuromuscular stretch
• heat-pain, temp, IF

Question 15

Kv2.1

Answer 15

-little inactivation and related to repol

Question 16

inward rectifier

Answer 16

-allow more current flow during hyperpolarization

Question 17

Ca activated K channel

Answer 17

-opens in response to Ca and sometimes depol

Question 18

channelopathies

Answer 18

Ca:
-congenital stationary night blindness
-familial hemiplegic migraine
-epoisodic ataxia type 2
Na:
generalized epilepsy with febrile seizures
K- benigne familial neonatal convulsion
-point mutations in transmembrane domain (pore)
-K channel is 4 of subunit

Question 19

Saxitoxin

Answer 19

-homologue of TTX

Question 20

a/b toxins

Answer 20

• scorpian
• prolong Na
• shift voltage of Na

Question 21

batrachotoxin

Answer 21

-inactivates Na channels

Question 22

dendrotoxin

Answer 22

wasps

• K channel blocker
• apamin from bees

Question 23

conotoxins

Answer 23

N type Ca channels

Question 24

agotoxin

Answer 24

spiders

P/Q type Ca channels

Question 25

active transporters

Answer 25

• translocate ions against gradient
• form complex with ion they transport
• binding/unbinding slow
• ion translocation is slower in transporters than channels