Chloride channels, transporters, and disease Flashcards
What do chloride ions do ?
involved in body fluid and cellular homeostasis
- electrolyte balance
- acid/base balance
- secretion
- cell volume regulation
they are important for many physiological functions
inhibitory synaptic transmission such as ligand gated glycine and gaba a receptor
What do inherited defects in chloride channel genes cause?
they cause human disease
Which proteins form chloride channels ?
they are made of up from multiple unrelated families- convergent evolution
- they are not like potassium channels that have evolved from 1 channel, chloride channels are varied
What are examples of ligand gated chloride channels ?
GABA a receptor
glycine recepotor
form inhibitory synapse
What are examples of intracellular chloride channels ?
CLC family = CLC3-7
-maintain pH and ionic content or organeles- endosomes/lysosomes
What are examples of voltage gated chloride channels ?
CLC family=1,2 Ka and Kb
- epithelial chloride transport
- membrane excitability
What are examples of calcium activated Cl- channels ?
bestrophin, tweety (TTYH1-4) TMEM16A and some calcium activated chloride channels
What are examples of ATP-binding cassette (ABC) transporter protein ?
CTFR, P-glycoprotein
- CFTR is the only member that forms an ion channel
What are the members of the CLC family ?
9 members
- 1-7 plus Ka and Kb - encoded by CLCN1-7 genes and CLCNKA and CLCNKB
- have 18 transmembrane alpha helices with some just dipping in and out
- Ka and Kb are kidney specific - suppose to be
they are largely pH sensitive and they have a wide range of properties
What functional studies of CLC channels have been carried out ?
CLC-0 of torpedo electrolyte
CLC-1= mammalian skeletal muscle
What structural studies of CLC channels have been done?
from bacteria and algae
What are the plasma membrane ClC- channels from the CLC family ?
CLC-1, 2, Ka and Kb
- ka and kb have a beta-subinit which act as an accessory protein
What are the vesicular cl-/H+ exchangers from the CLC family ?
CLC-3,4, 5, 6,7
the chloride ions and protons move in the opposite direction
Why are KO mouse models of CLC members made?
because many of these channels are linked to human diseases and therefore KO of the gene in mice is used to mimic disorders
What do CLC cl- currents look like ?
flicker between open and closed states
- look like they have a double barrelled pore
What are the differences between Kv channels and CLC channels ?
CLCs have 2 subunits while Kv channels have 4 subunits
Kv channels have a single ion conducting pore in the centre whereas CLC channels have 2 pores
in most channels like Kv the channels are modular in structure and have distinct structural domain such as pore domains, voltage sensor, inactivation gate, ligand binding domain
BUT
pore and activation domains are not as distinct in CLCs and are poorly understood
What currents are recorded from patch clamp experiments?
HEK293 cells transfected with either CLC-5 or human BKca demonstrated macroscopic CL- currents
- negative holding potential (-30 or -80mV) depolarising voltage pulses were applied
- larger the depolarisation the large the outward current recorded
- both give time dependent and outwardly rectifying macroscopic currents
What does outwardly rectifying current mean ?
there is more outward current than inward current
- outwad currents are carried by positively charged ions following out of the cell or negatively charged ions flowing into the cell
BKca and CLC-5 channels are pretty silent at negative potentials but as it depolarised the current increases