Ion Channels

Question 1

Where is Na and K concentration higher

Answer 1

Na outside cell
K inside cell

Question 2

How is RMP created

Answer 2

Differential Distribution of ions
- chemical disequilibrium is essential for life

Question 3

What maintains (establishes) the RMP

Answer 3

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

Question 4

Typical RMP of neuron

Answer 4

-70 mV

Question 5

Why is RMP -70 mV

Answer 5

Membrane more permeable to K than anything else, therefore RMP close to Ek

Question 6

ionic composition of typical cell

Answer 6

Na: extra- 135-147, intra- 10-15
K: extra- 3.5-5, intra- 120-150
Cl: extra- 95-105, intra: 20-30
(mEq/L)

Question 7

What is the driving force of an ion

Answer 7

Difference between the membrane charge and the equilibrium potential for a given ion
- electrochemical driving force acting on an ion
Vm- Eion

Question 8

How do ions flow at equilibrium potential

Answer 8

No net movement of that ion (E ion)

Question 9

What is plasma membrane permeable to

Answer 9

Small
Lipophilic
Uncharged

Question 10

Types of gated channels

Answer 10

Voltage gated- change in membrane potential
Ligand gated- chemical or hormone
Mechanically gated (stretch gated)- stimuli

Question 11

What is facilitated diffusion

Answer 11

Ion diffuse down their electrochemical gradient but do so by travelling through channel

Question 12

How are ion channels formed

Answer 12

Transmembrane protein
With central pore

Question 13

How are Nav and Cav pores formed

Answer 13

Monomers with four domains, 6 transmembrane spanning regions

Question 14

How to generate high resolution structures of ion channels

Answer 14

X-ray crystallography

Question 15

What regulates the ions that can permeate pore

Answer 15

Selectivity filter

Question 16

Who’s model looks like a physics diagram

Answer 16

Markov model

Question 17

Importance of nernst equation

Answer 17

Predicts the equilibrium potential of a single ion

Eion = 61/z * log (ion out/ ion in)

Question 18

What influences Eion

Answer 18

Concentration gradient
Membrane permeability
Ionic charge

Question 19

What is the importance of GHK equation

Answer 19

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

Question 20

Difference between GHK and Nernst Equation

Answer 20

• 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)

Question 21

Elements of HH Model, name scientists, importance

Answer 21

Alan Hodgkin and Andrew Huxley

1. Capacitor- plates correspond to inner and outer faces of membrane
2. Variable resistance (inverse of conductance)- gated ion channels shown with a switch
3. 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

Question 22

Why all all AP waves different in neuron

Answer 22

Many channel subtypes contribute to complex firing

Question 23

What channels do mammalian neurons generally express

Answer 23

2-3 Na channels
4-5 K channels (Ca activated)
2-3 Ca channels
HCN channel (auto rhythmicity)