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ELECTROPHYSIOLOGY & TRANSPORT: (Ion Channels (Examples of Interactions…
ELECTROPHYSIOLOGY & TRANSPORT:
Ion Channels
Properties
Families of Ion Channels
Voltage Gated
Generating RMP
Requires the K+ ion concentration to be greater inside cell.
Cell membrane must be permeable to K+ by having K+ ion channels that are open.
Transmitter Gated
Closed, open active, open inactive (desensitised)
Gating of channels
Voltage Gated
Ligand Gated
Mechanically Gated
Measurement of Channel Function by Patch Clamping
Capacitance changes as a result of vesicle exocytosis
Currents across single channels (open probability)
Membrane Potentials
Intracellular Ion Concentrations
Distribution of Charges
Generating Resting Membrane Potentials
i. Cell membrane is permeable to K+
Evidence that K+ diffusion potential is involved.
Altering the K+ gradient by changing the K+ concentration outside the cell directly changes the RMP.
A K+ channel inhibitor such as Ba2+ ion (barium ion) causes a fall in the resting membrane potential (RMP) of a cell.
ii. Cell membrane is impermeable to Na+
iii. Na+, K+-pump maintains ion concentration gradients
iv. Na+ K+-pump is the main electrogenic transport pump. It pumps three Na+ ions out for every two K+ ions in.
Mechanically Gated Channel
Ca2+ release channel of SR (ryanodine receptor)
Stretch-activated Cl- channels (cell volume control)
Examples of Interactions Between Channels
Neuromuscular junction ion channels
Ion Channels in Muscle Contraction
Action potentials
Electrophysiology of Adaptation and Memory
Synaptic Transmission
Post-synaptic potentials (PSPs)
Ligand Gated Channel
Carriers and Pumps
"Master Pump" of Animal Cells - Na+ K+-ATPase (sodium pump)
"Master Pump" of Plant Cells and Bacteria
Families of Transporters
Sodium or Hydrogen Gradient-Driven Pumps - “Porter Systems”
Regulation of Transport Activity
Changes in Ion Concentrations, pH, or Voltage around Channel (Biochemical)
Control of Synthesis or Degradation - e.g. aldosterone, organic osmolyte transporters
Protein-Protein Interactions - K+ channel, sulfonyluria receptor, and Ca2+v channel
Control of Insertion or Removal - e.g. SGLT, GLUT4, ENaC, AP2
Phosphorylation or Dephosphorylation:
Autoinhibition
Transport Related Diseases
Ion Channel Diseases
Pump Diseases