Goldman Hodgkin-Katz

equilibrium

unchanging state that remains so without manipulation

steady state

unchanging state that remains so only by constant input or output

Is the membrane permeable to more than one ion at rest?

yes, but K+ efflux dominates

Is the membrane at equilibrium or in a steady state?

in a steady state, the membrane can only be at one potential

V_m

the cell membrane potential at which the net flux of all ionic together is equal to 0

GHK equation

• used to find Vm

• if a cell is permeable to multiple ions, the Vm is a weighted average of the Ex for each permeable ion

multiple-ion case application

the V_m is somewhere between the MOST negative E_x (usually E_K) and the MOST positive E_x (usually E_Na)

one-ion case

• GHK reduces to the Nernst

• V_m approximates to E_x of the most permanent ion

What is GHK’s connection to the Nernst?

• for an AP, the membrane becomes briefly VERY permeable to Na⁺ so the V_m approaches E_x

What drives AP?

• permeability changes

• ions with a greater permeability have great influence on V_m

  • the larger the influence of the ion, the close V_m will be to E_x

At rest, what is the membrane mostly permeable to? What does this mean?

mostly permeable to K+ so the V_m is close to E_k

What does Cl^- do in AP?

plays a role in maintaining rest and in synaptic potentials