WSC331 Bioelectricity Quiz

Bioelectricity and Biophotonics Engineering

• Course code: WSC331
• Lecturer: Felipe Iza
• Email: [email protected]
• Institution: Loughborough University, U.K.

Recap from previous lecture

• Intracellular medium contains anions (A-), potassium (K+), and sodium (Na+); extracellular medium contains chloride (Cl-) and sodium (Na+).
• Ion distribution and membrane potential are key bioelectric properties.
• The Goldman-Hodgkin-Katz equation explains the resting potential, considering ion permeabilities (conductances).

Nernst and resting potentials

• Nernst Potential: Equilibrium transmembrane potential for a single ion.

  • Calculates the electrical potential needed to balance the concentration gradient of an ion across a membrane.
  • Uses the formula: E = (RT/zF)ln(C_o/C_i)
    • where: E = equilibrium potential, R = ideal gas constant, T = absolute temperature, z = valence of ion, F = Faraday constant, Co = extracellular concentration, Ci = intracellular concentration

• Resting Potential: Equilibrium transmembrane potential when multiple ions are present.

  • Weighted average of Nernst potentials based on ion conductances.
  • Goldman-Hodgkin-Katz equation: Vm = (g_KE_K + g_NaE_Na + g_ClE_Cl)/(g_K + g_Na + g_Cl).
    • where Vm = membrane potential, g = conductance, E = Nernst potential.

Example - Squid axon

• Intracellular and extracellular ion concentrations (mM) for potassium (K+), sodium (Na+), and chloride (Cl-).
• Conductances (mS/cm²) for K+, Na+, and Cl-
• Calculation examples for resting potential, net current, and ion flow across the membrane are provided.

Answer

• Nernst potentials for K+, Na+, and Cl- are calculated using provided data.
• The resting membrane potential (Vm) is calculated using the Goldman-Hodgkin-Katz equation.
• The resting membrane potential for a squid axon is approximately –68mV

Ionic currents

• Vm > EK: Potassium efflux (IK > 0)
• Vm < ENa: Sodium influx (INa < 0)
• Vm < ECl: Chloride efflux (ICl < 0)

So far...

• Key components of the membrane (capacitive nature of the phospholipid bilayer, ion channels, ion conductances)
• Nernst potentials for each ion species.

Today's lecture

• Transport phenomena across cell membranes
• Quasineutrality
• Donnan equilibrium
• Role of pumps

Quasineutrality

• Concentrations of anions must equal concentrations of cations for a zero net charge.
• Imbalance results in large electric fields that restore the zero net charge.
• Membrane charges reside on the membrane, not within the solution.

If quasineutrality did not hold...

• Example calculating the electric potential in the center of an organ given parameters.
• Calculations using Poisson's equation.
• Boundary conditions to solve the equation.

Donnan equilibrium

• Equilibrium condition where all permeable ions are individually in equilibrium.
• Equation: Ik = INa = ICl = 0.
• Concentration conditions required for Donnan equilibrium.

Exercises

• Questions about final concentrations and transmembrane potential when the membrane is permeable to all ions.
• Exercises and answers are given for both permeable and semipermeable membrane conditions and calculations.

Answers-comparison

• Comparison of results for permeable vs. semipermeable membrane calculations.

Relative depletion charge

• Equilibrium is reached through ion movement.
• Nernst equilibrium: concentrations stay constant.
• Donnan equilibrium: concentrations change.
• Exercise describing the transmembrane potential for typical changes in charge.

Relative charge depletion

• Typical values for capacitance (C) and areas.
• Typical intracellular K concentration.
• Charge in the electrolyte.

Role of pumps

• E_K and E_Na are different, resulting in unequal influx and efflux.
• The steady resting sodium and potassium flux change intracellular concentrations.
• The Na-K pump maintains stable concentrations.

Transport across the membrane

• Summary of transport mechanisms (diffusion, conduction, pumps) across the cell membrane
• Membrane potential and electro-chemical gradients
• Explanation of ion fluxes in and out of the cell

Recap: Different equilibriums

• Nernst potential for single ions.
• Resting potential for multiple ions (Goldman equation)
• Donnan equilibrium and conditions.
• Which equilibrium in living cells.

Today's lecture

• Summary of today's lecture topics.
• Includes: Transport phenomena, quasinentrality, Donnan equilibrium, role of pumps.

Tutorial Questions

• The exercises to be completed and the URL for the learning platform.

Test your understanding of bioelectricity and biophotonics engineering in this quiz based on course WSC331. Topics include ion distribution, membrane potential, Nernst potential, and the Goldman-Hodgkin-Katz equation. Assess your grasp of key concepts and equations used in the study of bioelectrical properties.