Channels and Transporters

Question 1

What does microscopic current measure?

Answer 1

1 channel

Question 2

What does Macroscopic current measure?

Answer 2

the sum of all the channels

Question 3

how do you measure just the K+ channel without measuring the Na+ channel?

Answer 3

block the Na+ channel by adding TTX (tetrodatoxiN)

Question 4

how do you measure just the Na+ channel without measuring the K+ channel?

Answer 4

block the potasaIUM channel by adding TEA (tetra ethyl ammonIUM)

Question 5

what are 3 characteristics of voltage gated channels?

Answer 5

they are all or none ( wither closed or open)
they open and close randomly ( stochastically)
if you change the voltage you can increase/decrease the probability that the channels will be open/close

Question 6

what happens to current as depolarization increases?

Answer 6

there is a larger inward current

Question 7

what does the patch clamp technique record?

Answer 7

microscopic currents

Question 8

what did the patch clamp technique provide the first evidence of?

Answer 8

single channels

Question 9

what is gating?

Answer 9

the transition between open and closed states ( a jump in current)

it involves temporary conformational change in the channel’s structure

Question 10

depolarization increases the probability that which channel will be open?

Answer 10

Na+ channel ( see pg. 115)

Question 11

Why do K+ channels have a sustained response i.e. greater maintenance of outward current compared to Na+’s rapid inward current?

Answer 11

because the K+ gate usually can only close it can’t inactivate like Na+ can and closing takes longer to happen whereas inactivation is quick. thus K+ generally doesn’t induce a refractory period like Na+.

Question 12

are the properties of the microscopic currents the same or different than the macroscopic currents?

Answer 12

they are the same

Question 13

what produces the diversity in the spike waveforms and patterns exhibited by different cells?

Answer 13

the diversity of K+ channels: some inactivate, some inactivate quickly, some don’t inactivate

Question 14

how do BK channels inactivate?

Answer 14

rapidly ( BK is fast like burger king)

Question 15

BK is activated by?

Answer 15

calcium and depolarization

Question 16

how do medium after hyperolarization K+ channels (AHP) work?

Answer 16

they control the early interspike interval ( they are slowly activating by Ca2+ entry.

***they don’t inactivate

Question 17

how do slow after hyperolarization K+ channels (AHP) work?

Answer 17

they limit firing frequency by an unknown channel, which affects the action potential

***they do not inactivate

Question 18

which channel only allows through a single type of ion through the channel ( generally speaking , b/c there are some exceptions)?

Answer 18

voltage gated channels

Question 19

what type of chanel often lets through two or more types of ions through a channel?

Answer 19

ligand gated ion channels

Question 20

Why is there so much diversity in K+ channels?

Answer 20

because there are hundreds of genes encoding K+ channels and the splicing variations produce different characteristics in the channels ALTHOUGH most ion channels don’t vary much in fnc.

Question 21

which K+ channel plays a tumorigenic role in human mammary cells?

Answer 21

Kv4.1 ( it is voltage gated)

Question 22

Where is Kv1.4 prominent?

Answer 22

in the medial perforate path in the middle molecular layer of the DENTATE GYRUS, and mossy fiber axons and terminals of the S.LUCIDUM of CA-3

Question 23

Where is Kv2.1 prominent?

Answer 23

PYRAMIDAL cell CA-1 layer

Question 24

What do Kv2.1 do and what type of inactivation do they exhibit?

Answer 24

they are related to channels involved in repolarization and they show little inactivation.

Question 25

what do Kv4.1 channels do?

Answer 25

they inactivate rapidly to depolarize.

Question 26

K+ inward rectifying channels allow more current do flow during?

Answer 26

hyperpolarization than during depolarization

Question 27

4 channels together can make a _______ ________?

Answer 27

passive pore

Question 28

what component of an ion channel can impart voltage sensitivity to close or open a channel?

Answer 28

the transmembrane alpha helix loop

Question 29

what is a channelopathy?

Answer 29

a genetic disease resulting in a mutation in channel genes.

Question 30

what are some voltage gated Calcium channelopathies?

Answer 30

congenital stationary night blindness
familial hemiplegic migrane ( x-lined recessive)
episodic ataxia type 2

Question 31

what are doe Na+ channelopathies?

Answer 31

generalized epilepsy w/ febrile seizures

Question 32

What are some K+ channel channelopathies?

Answer 32

Benign familial neonatal convulsion

Question 33

How does the structure of K+ compare to that of Ca2+ and Na+?

Answer 33

it is a 5-7 transmembrane domains whereas Ca2+ and Na+ have many more.

Question 34

what does Saxitoxin do?

Answer 34

like TTX it blocks Na+

Question 35

what does alpha toxin do?

Answer 35

prolong the duration of Na+ currents

Question 36

what does beta toxin do?

Answer 36

shift the voltage activation of Na+ channels

Question 37

what does Batrachotoxin do?

Answer 37

inactivate Na+ channels

Question 38

what does Dendrotoxin do and where is it found?

Answer 38

block K+ channels , it’s found in wasps

Question 39

what does Apamin do and where is it found?

Answer 39

It blocks K+ channels and is found in bees.

Question 40

what do ion exchangers use for energy?

Answer 40

concentration gradients NOT ATP

Question 41

Is ion translocation slower or faster in transporters than it is in channels?

Answer 41

slower in transporters than in channels