Ion Channels & Transporters

Question 1

Ion channels

Answer 1

use concentration and electrical gradients; allow diffusion
usually selective for specific ions; permeability
most gated by signals (chemical/electrical)

Question 2

Voltage gated ion channels

Answer 2

Na+ ; out->in
Ca2+; out->in
K+; in->out
Cl-; out->in

Question 3

ligand gated channels

Answer 3

neurotransmitter receptor
ca2+ activated K+ channel
cyclic nucleotide gated channel (cAMP, cGMP, GCPR); K+ outward, Na+ inward
VR-1 receptor; capsaicin

Question 4

measuring ion channel activity

Answer 4

cell-attached recording
whole cell recording
inside out recording
outside-out recording

Question 5

measuring single Na+ channel

Answer 5

short, quick response; inward; early

closed->(depolarization) open->inactivating->inactivated (hyperpolarized)->closed

Question 6

measuring single K+ channel

Answer 6

delay, long lasting response; outward; later

closed->(depolarization) closed->open->open (hyperpolarized)->closed

Question 7

transporters

Answer 7

ions/small molecules against their gradients/electrochemical concentration/ electrical potential
require energy; ATP
creation of ion concentration gradient

ATPase pumps - NA+/K+ pump, Ca2+ pump(use H+)
Ion exchangers - Na+/Ca2+ exchanger, Na+/K+/Cl- cotransporter, K+/Cl- cotransporter, Na+/H+ exchanger, Na+/neurotransmitter transporter (Na+ and GABA,Dopamine)

Question 8

Na+/K+ ATPase

Answer 8

[Na+] greater out than in
[K+] greater in than out
3Na+out 2K+in
Electrogenic; cell negative inside
Na+ bind -> ATP hydrolysis&phosphorylation -> K+ bind -> dephosphorylation

Question 9

Ouabain

Answer 9

inhibit Na+/K+ ATPase

post stimulus hyperpolarization blocked

Question 10

Ca2+ pump

Answer 10

ATP binds with Mg2+, 2 Ca2+ in place
phosphorylation
2 Ca2+ and ADP detached. 2H+ in place
Mg2+ and P detached 
2Ca2+ comes in,
2H+ detached

Question 11

Transporters

Answer 11

do not use ATP

Uniporter; glucose, amino acids
(cotransporter) symporter & antiporter - one against gradient, one down gradient

neurotransmitter&precursor taken into nerve/vesicle via a transporter

• EAAT; excitatory amino acid transport; glutamate from cleft to nerve
• VGLUT; vesicle glutamate transport; glutamate from terminal into vesicle
• VIATT; vesicle inhibitory amino acid transporter; GABA into vesicle
• Glycine transporter; ?

Question 12

topology of voltage gated Na+ channel and K+ channels

Answer 12

Na+ channel; 4 domain monomer
K+ channel; tetramer

• Ca2+ channel; similar to Na+ channel

Question 13

K+channel

Answer 13

tetrameric protein
6 sub domains
1 pore-segment

sub domain 4 contains (+) residues; voltage sensor
N-terminal (4) is inactivating segment

Question 14

Na+ channel

Answer 14

monomeric
4 homologous domains
structurally like K+ channel subunits
one inactivating domain between III&IV domains
analogous S4 domain are voltage sensors