Unit 2 - Ion Flux and Resting Membrane Potential

Isopotential

Membrane potential is uniform

Goldman Hodkin Katz Equation

P_K

1

P_Na

0.04

P_Cl

0.45

K_i

125mM

K_o

5mM

Na_i

12mM

Na_o

120mM

Cl_i

5mM

Cl_o

125mM

EQ must consider both

Osmotic balance and electrochemical gradient

What causes swelling?

Imbalanced negative charge causes Na to enter and H₂O to follow

Gibbs-Donnan EQ

If solutes are separated by a membrane impermeable to 1 species, solutes become unequally distributed between to area to make new EQ

Gibbs-Donnan EQ Requirements

1. [cation] = [anion] in ECF and ICF to maintain charge balance

2. At EQ, products of [permeable ion] outside = inside

3. E_m = E_k = E_Cl

Purpose of Na/K

Counters impermeable ion effect and maintains V_M

Cyanide

Stops mitrochondrial ETC from making ATP, therefore stopping Na/K pump

Capacitance

Ability of cell membrane to separate charge

The ICF and ECF are like

Conductors

The channels are like

Resistors

The cell membrane is like

Capacitor that holds/separates charge of ICF and ECF

Cell Membrane Capacitance

10^-6F/cm²

1cm equals

10 000um

1 pico equals

10^-12

1mL equals

1cm³

1L equals

1000cm³

y_ion

Conductance of a single ion

g_ion

Conductance of all channels

Driving Force Equation

I = g_ion(V_m-E_k)

If I is negative

Ion will enter cell if it's a positive ion

If I is positive

Ion will leave the cell if it’s a positive ion

Reversal Potential

Specific membrane voltage where current_net flow through a channel reverses direction and equal 0