Ion Channels Flashcards
Where is Na and K concentration higher
Na outside cell
K inside cell
How is RMP created
Differential Distribution of ions
- chemical disequilibrium is essential for life
What maintains (establishes) the RMP
Na/K atpase - distribution of Na/ K - 3 Na out, 2 K in - cause depletion of positive charge in cell
K leak channels
Resting permeability to Na and Cl
Typical RMP of neuron
-70 mV
Why is RMP -70 mV
Membrane more permeable to K than anything else, therefore RMP close to Ek
ionic composition of typical cell
Na: extra- 135-147, intra- 10-15
K: extra- 3.5-5, intra- 120-150
Cl: extra- 95-105, intra: 20-30
(mEq/L)
What is the driving force of an ion
Difference between the membrane charge and the equilibrium potential for a given ion
- electrochemical driving force acting on an ion
Vm- Eion
How do ions flow at equilibrium potential
No net movement of that ion (E ion)
What is plasma membrane permeable to
Small
Lipophilic
Uncharged
Types of gated channels
Voltage gated- change in membrane potential
Ligand gated- chemical or hormone
Mechanically gated (stretch gated)- stimuli
What is facilitated diffusion
Ion diffuse down their electrochemical gradient but do so by travelling through channel
How are ion channels formed
Transmembrane protein
With central pore
How are Nav and Cav pores formed
Monomers with four domains, 6 transmembrane spanning regions
How to generate high resolution structures of ion channels
X-ray crystallography
What regulates the ions that can permeate pore
Selectivity filter
Who’s model looks like a physics diagram
Markov model
Importance of nernst equation
Predicts the equilibrium potential of a single ion
Eion = 61/z * log (ion out/ ion in)
What influences Eion
Concentration gradient
Membrane permeability
Ionic charge
What is the importance of GHK equation
Goldman Hodgkin Katz equation
- predicts membrane potential using multiple ions
- Vm is determined by combining contributing concentration gradients and membrane permeabilities of each ion
Vm = 61* log (Pk[K out] + PNa[Naout] + PCl[Cl in])/in +in +Cl out
Difference between GHK and Nernst Equation
- GHK takes into account permeability of plasma membrane for that ion (Nernst doesn’t)
- Z in Nernst took into account charge, GHK doesn’t so Cl flipped in/ out (Na out/ in)
Elements of HH Model, name scientists, importance
Alan Hodgkin and Andrew Huxley
- Capacitor- plates correspond to inner and outer faces of membrane
- Variable resistance (inverse of conductance)- gated ion channels shown with a switch
- Electromotive forces- separation of charged ions across the cell membrane set up by Na/K ATPase activity
Na/K ATPase sets up battery, battery drives current and separates charge
Importance contribution to phospholipid bilayer
Why all all AP waves different in neuron
Many channel subtypes contribute to complex firing
What channels do mammalian neurons generally express
2-3 Na channels
4-5 K channels (Ca activated)
2-3 Ca channels
HCN channel (auto rhythmicity)