ion channels

• What does the Na/K ATPase pump do?


  Pumps 3 Na⁺ out for 2 K⁺ in
• Why is the resting membrane potential (RMP) negative?


  Because K⁺ exits the cell through specialized channels
• What does the electrical driving force do for potassium ions?


  It attempts to bring potassium back into the negatively charged cell
• What happens if the electrical gradient is strong enough?


  It creates equilibrium with the chemical gradient
• What does the Nernst equation calculate?


  Equilibrium potential
• What does the Goldman equation calculate?


  Membrane potential when more than one ion is involved
• What does a slope in an IV plot indicate?


  It reflects the relationship between current flow and membrane voltage
• What is the purpose of a 2-electrode voltage clamp?


  To record membrane currents
• What type of cell is often used in voltage clamp experiments?


  Oocyte cell
• What does whole-cell mode detect?


  Small changes in membrane potential and action potentials
• How can current be injected into a cell during voltage clamp experiments?


  Through the pipette
• What is the phenomenon of rectification in ion channels?

  Channels pass current better in one direction than the other
• What causes the resting membrane potential to change in vivo neurons?


  K⁺ leak currents, persistent sodium currents, and synaptic outputs
• How do ion channels facilitate ion flow?

  By having an aqueous pore that substitutes for water
• What happens to K⁺ ions when they pass through ion channels?


  They are dehydrated and substitute for water
• Why can't smaller Na⁺ ions pass through K⁺ channels?

  Because they do not interact efficiently with the carbonyl residues in the pore
• What are the characteristics of leak channels?


  • Moderate conductances
  • Always partially open
  • Provide baseline excitability
  • Not suitable for fast electrical events
• What are the characteristics of gated channels?


  • Open/close for specific stimuli
  • Changes in membrane potential
  • Binding of a ligand
  • Physical impacts (temperature or pressure)
• What are the two types of potassium channels responsible for resting membrane potential generation?


  Inward rectifier K⁺ channels (Kir) and tandem pore K₂P channels (TWIK)
• How do inward rectifier K⁺ channels (Kir) function?


  They pass K⁺ ions into the cell better than out
• What is the assembly structure of Kir channels?


  They assemble into tetramers (4 subunits)
• What is the effect of anaesthetics like isoflurane on TWIK channels?


  They open various TWIK channels and hyperpolarize them
• What is the membrane potential of astrocytes?


  • 80 mV
• What types of channels do astrocytes express?


  4TM leaks from TWIK and inward rectifiers
• How does high K⁺ conductivity affect astrocytes?


  It makes them unable to propagate electrical charges on membranes
• What mediates depolarization during action potentials?

  An influx of sodium
• What are the two factors affecting resting membrane potential (RMP)?


  Leak channels and persistent sodium currents
• How do persistent sodium channels affect respiratory circuits?


  They underlie oscillatory behavior in brain stem respiratory circuits
• What is the significance of sodium leak in neurons?


  It keeps some neurons constantly active in the CNS
• What is the membrane potential of astrocytes?


  • 80 mV
• What type of potassium channels do astrocytes express?


  4TM leaks from TWIK (KCNK sub-family - KCNK1) and inward rectifiers
• Why can't astrocytes propagate electrical charges on membranes?


  High K+ conductivity makes them unable to do so
• What mediates depolarization during an action potential (AP)?

  An influx of sodium ions
• How are sodium channels controlled?


  By the potential of the membrane
• What happens to sodium channels when the membrane potential becomes positive?


  The sodium channels become inactivated
• What is the reversal potential for sodium?


  60 mV
• At what membrane potential is the sodium channel activated?


  • 40 mV
• What is the role of the inactivation gate in sodium channels?


  It allows a certain number of sodium ions to pass before blocking
• What limits the maximum frequency of action potentials?

  Inactivation of voltage-gated sodium channels
• What is the basis for the absolute refractory period?

  It is due to the inactivation of sodium channels