Ion channels Flashcards
Primary pumps
Use ATP to pump ions against a electrochemical gradient
Ions are usually H+ or Na+
establish gradients for driver ions
Carriers
Can be energised by driver ions (secondary active transport)
Symporters/co-transporters
Antiporters
Facilitators (not energised) facilitate passive diffusion down gradient
Channels
Always passive transport down gradient Highly regulated (defined open and shut gating) Selective for specific ions
Permeation
Permeant ions are able to move through when the channel opens
Direction and rate of movement governed by electrochemical gradient
Selectivity
Non-selective are permeable to anions and cations Anion selective (glycine receptor) have ring of positively charged residues Cation selective (Ach receptor) have ring of negatively charged residues Some channels able to discriminate between cations (K+ selectivity based on hydration energy)
Gating
Influenced by changes in membrane voltage (voltage gated) Ligand gated (acetyl choline receptors) Mechano-sensitive Changes in temperature
Modulation
Modulators influence gating following activation (do not gate channel)
Ca2+, H+, ATP, fatty acids
Accessory proteins
Tightly associated with the channel Specify location and abundance (Rapsyn clusters AchR at excitatory synapses) Modulate gating (SUR subunit of Katp channel hydrolyses ATP to stimulate opening)
Kir channel family
K+ inward rectifiers
Includes ATP-sensitive and G-protein coupled channels
Regulate membrane voltage
Two pore K+ channel family
Arose from tandem duplication of Kir dimers
Represent leak K+ channels (set membrane voltage to Ek in most cells)
Glutamate receptor family
All cation permeable
Tetramers
Pore loop in inverse direction
Subfamilies defined by preferred agonist (AMPA, Kainate, NMDA)
Voltage gated family
S4 voltage sensor (depolarisation)
Kv subfamily involved in K+ efflux, repolarisation of action potential
NaV subfamily Na+ influx, AP depolarisation
CaV subfamily Ca2+ signalling
SK/BK family
Ca2+ activated K+ efflux channels
Neuron repolarisation
SK small, voltage insensitive
BK large, activated by depolarisation and Ca2+
TRP family
Promiscuous activation
Voltage insensitive
Sensory perception
CNGC family
Photo and olfaction reception
Activated by direct binding to cyclic nucleotides (CNs)
Modulated by voltage
HCN family
Activated by hyperpolarisation
CN modulated
Cys-loop receptor family
Non pore-loop family
Pentamers
Pore formed by TMS2
AChR (cation permeable) at neuromuscular junction
GABA (Cl- permeable) at inhibitory synapse
GlyR glycine receptors (Cl- permeable) at inhibitory synapse in brain
5HT serotonin receptors (cation permeable)
IP3/RYR receptor family
Major intracellular Ca2+ release channels
Endomembrane location
RYR (muscle contraction)
IP3 receptor has myriad of Ca2+ signalling roles
CLC family
Anion selective
CLC1 at plasma membrane in skeletal muscle
CLC5 at endomembrane provides shunt conduction
CFTR
ABC (ATP binding cassette) transporter
Epithelial transport (lungs, intestinal tract)
Involved in cystic fibrosis
Bestrophin family
Anion selective
Ca2+ activated
Form tetramers, TMS2 forms pore
Possible plasma membrane and endomembrane location
Anoctamins
Cl- selective
Ca2+ activated
Found in almost all animal cells
Epithelial fluid secretion and control of smooth muscle contraction
