g2009A12 Outline the factors contributing to the generation and maintenance of the
resting membrane potential.

· Intro: RMP

· Generation and maintenance

· Equations

· Normal ion concentrations and Nernst potentials

Definition

· The potential difference between ICF and ECF when there is no net ion flux

By cell type

· Muscle: -90mV

· Neuron: -70mV

· Cardiac pacemaker cell: -60mV (but not static)

· Smooth muscle: wandering -40 to -60mV

Effective barrier

· Lipid bilayer with polar phospholipid heads, non-polar fatty acid tails

o Freely permeable to water, gases but not ions

· Ion channels

o Activity tightly regulated by ligands or membrane potential difference

o Ion flux upon opening is determined by electrochemical gradient

Differential ion concentrations

· Na⁺K⁺ATPase (major)

o Electrogenic

o Energy requiring

o Continuously active

· Gibbs-Donnan effect (minor)

o Anionic proteins predominate

o Attracts permeable cations i.e. K⁺

Differential permeability

· K⁺ permeable at rest (hence most RMPs closest to K⁺’s Nernst potential)

· Na⁺ impermeable at rest

Nernst

E = RT/zF x log_e ( [ion]_o/[ion]_i )

· Calculates PD resulting from complete permeability for a given ion (see below)

Goldman-Hodgkin-Katz

· Calculates PD resulting from existing permeabilities ion concentrations