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

 

List:

·         Intro: RMP

·         Generation and maintenance

·         Equations

·         Normal ion concentrations and Nernst potentials

 

Intro: resting membrane potential

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

 

Generation and maintenance of RMP

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

 

Equations:

Nernst

E = RT/zF x loge ( [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

 

Normal values:

 

ICF concentration

ECF concentration

Nernst potential

Na+

10mM

140mM

+60mV

K+

150mM

4mM

-90mV

Cl-

15mM

110mM

-65mV

 

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