Week 3 (Equations, Driving force)

Nernst Equation

• Formula for calculating the individual equilibrium potentials for each ion

  • The equilibrium potentials occurs when the electrical and concentration gradiants are balanced

  • There is no net flow of an ion

The Approximate Equilibrium Potentials for each Ion

• Potassium

  • -85mV

• Sodium

  • +65mV

• Chloride

  • -72mV

• Calcium

  • +135mV

Goldman Equation

• Formula for calculating the membrane potential

• Takes into account the equilibrium potentials of ALL ions and their permeabilities

• Vm = membrane potential voltage

• P = relative permeability

• Permeability refers to how easily that ion can cross the membrane

  • it is directly proportional to how many channels there are for that ion

  • Relative permeability usually revolves around potassium

  • Permeability can change

Driving Force

• To predict how ions will move when ion channels open

• We can calculate the Driving force for each ion

• Driving force = membrane voltage - equilibrium

• The sign of the driving force tells you efflux or influx

• The magnitude tells you how much force there is favoring influx or efflux

Vdf = Vmembrane (Vm) - Eion