Lecture 3

• According to the diagram, is the intracellular (IC) side positive or negative relative to the extracellular (EC) side with contribution from K+ channels?

  Negative
• What characterizes the equilibrium state regarding ion movement?

  Movement out equals movement in
• What is indicated when there is no net flow of ions?

  No current flow
• In the context of K+ channels at equilibrium, what type of electrical potential is established?

  Negative potential
• What does the Nernst equation calculate?

  Equilibrium potential for an ion
• What does 'R' stand for in the Nernst equation?

  Gas constant
• What does 'T' represent in the Nernst equation?

  Temperature in Kelvin
• What does 'Z' stand for in the Nernst equation?

  Valence of the ion
• What does 'F' represent in the Nernst equation?

  Faraday's constant
• If a membrane is purely selective to $K^+$, what does $V_m$ equal?


  $E_K$
• What is the extracellular concentration of $K^+$ provided?


  5 mM
• What is the intracellular concentration of $K^+$ provided?


  140 mM
• What is the $E_K$ for a purely $K^+$ selective membrane?


  -89 mV
• What is the membrane potential $V_m$ for a purely $K^+$ selective membrane?


  -89 mV
• What does the variable 'z' represent in the simplified Nernst equation $E_{ion} =$$\frac{61.5}{z} \times \text{Log} \frac{[\text{ion}]_{out}}{[\text{ion}]_{in}}$?


  The ion's valence
• What is the calculated Nernst potential for sodium, given the provided concentrations?

  +61.5 mV
• According to the diagram, is the intracellular (IC) side positive or negative relative to the extracellular (EC) side with contribution from $Na^+$ channels?


  Positive
• For a purely $Na^+$ selective membrane, what does $V_m$ equal?


  $E_{Na}$
• What is the extracellular concentration of $Na^+$ provided?


  150 mM
• What is the intracellular concentration of $Na^+$ provided?


  15 mM
• What is the $E_{Na}$ for a purely $Na^+$ selective membrane?


  +61.5 mV
• What is the membrane potential $V_m$ for a purely $Na^+$ selective membrane?


  +61.5 mV
• How does the cell membrane potential change based on the relative contribution of $K^+$ and $Na^+$ channels?


  It moves between $E_K$ and $E_{Na}$
• What factors determine the membrane potential?

  Bioelectricity and ion channels
• What is the extracellular concentration of $Cl^-$ provided?


  102 mM
• What is the intracellular concentration of $Cl^-$ provided?


  4 mM
• What is the $E_{Cl}$ value?


  -87 mV
• What is the valence (z) of chloride in the Nernst equation?

  -1
• What is the relative selectivity of the $K^+$ channel?


  50-75
• What is the relative selectivity of the $Na^+$ channel?


  1
• What two factors does the Goldman equation take into account?

  Concentrations and selectivity
• What does the Goldman equation predict?

  Membrane potential
• Using the 50 to 75 x more selective values, what range does $V_m$ fall within?


  -78 to -82 mV
• How is the resting membrane potential of -70 mV maintained in a cell?

  Movement at $V_m$
• What type of transporters are voltage-gated $Na^+$ and $K^+$ channels?


  Electrogenic transporters
• What physiological principle does the selectivity of ion channels relate to?

  Membrane potential
• How many times more selective is a $K^+$ channel than a $Na^+$ channel?


  ~50 times
• How many times more selective is a $Na^+$ channel than a $K^+$ channel?


  ~5 times
• What can impact exact values of selectivity of ion channels?

  Tissue and ionic concentrations
• What does cotransport of Na+ with phenylalanine show?

  $Na^+$-amino acid cotransport