Ion Channels & Transporters Flashcards
Ion channels
use concentration and electrical gradients; allow diffusion
usually selective for specific ions; permeability
most gated by signals (chemical/electrical)
Voltage gated ion channels
Na+ ; out->in
Ca2+; out->in
K+; in->out
Cl-; out->in
ligand gated channels
neurotransmitter receptor
ca2+ activated K+ channel
cyclic nucleotide gated channel (cAMP, cGMP, GCPR); K+ outward, Na+ inward
VR-1 receptor; capsaicin
measuring ion channel activity
cell-attached recording
whole cell recording
inside out recording
outside-out recording
measuring single Na+ channel
short, quick response; inward; early
closed->(depolarization) open->inactivating->inactivated (hyperpolarized)->closed
measuring single K+ channel
delay, long lasting response; outward; later
closed->(depolarization) closed->open->open (hyperpolarized)->closed
transporters
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)
Na+/K+ ATPase
[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
Ouabain
inhibit Na+/K+ ATPase
post stimulus hyperpolarization blocked
Ca2+ pump
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
Transporters
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; ?
topology of voltage gated Na+ channel and K+ channels
Na+ channel; 4 domain monomer
K+ channel; tetramer
- Ca2+ channel; similar to Na+ channel
K+channel
tetrameric protein
6 sub domains
1 pore-segment
sub domain 4 contains (+) residues; voltage sensor
N-terminal (4) is inactivating segment
Na+ channel
monomeric 4 homologous domains structurally like K+ channel subunits one inactivating domain between III&IV domains analogous S4 domain are voltage sensors