ion chanel fundamentals

Protein classes at the plasma membrane

• trasnporters

• Linkers

• Receptors

• Enzymes

Ion cahnnels

Transporter ions across the plasma membrane

What do ion channels regualte

Membrnae potenital

Membrane potential

The difference in electrical potential between interior and the exterior of a cell

Types of ion channels

• channel protein

• Carrier protein

• Pump

Membrane potential

Voltage difference between the inside and outside of a cell that only exists at the plasma membrane and arises from differences in ionic concentration across the plasma membrane

What is teh equilibrium potential also known as

Reversal potential/ Nernst potential

When will diffusion across memrbane continue until

The electrical force is equal to the chemcial froce → equilibrium

What is the reversal potenital

The point at which ions swap direction of movement

Nernst potential full

Eion= RT/ZF ln(ion 1/ion 2)

What are each of the letters in the Nernst potenital

• r= gas constant

• T= absolute temperature

• z= valence of ion

• F= faraday constant

What is the simplified enernst potential equaiton

Eion= 60/z log10(ion out/ ion in)

For example of na Nernst potnetial eqtn

E Na= 60 log 10( na out/ na in)

What are ion channels best understood id

In terms of their reversal potential

What does the Nernst potential “transalte”

Translates the chemcial gradient into an electrical force

What is teh Goldman Hodgkin Katz equation

A reorganised Nernst equation for na, cl and k → are key determinants of memrbane potential

What does teh Goldman Hodgkin Katz equaiton says

That memebrane potential is weighted avergae of the K, Na and Cl mepemraben potentials

What is the Goldman Hodgkin Katz equation for k,na and cl

Em= rt/f ln (Pk[k+] out + Pna[na+] out + Pcl[Cl+-] in / pl[k+ in + Pna [na+]in + Pcl [Cl+-] out)

What is teh Em

The weighted average of the contributing ion channels reversal potentials

At rest what does Em tend towards and why

Ek→ most ion cahnnels are K+ at rest

During an action potential what doe Em tend towards

ENa

Steps fo the sodium potassium pum (6)

• cytoplasmic Na+ binds to the Na+/K+ pump

• The Na+/K+ pump is phosphorylated by ATP

• The pump changes its conformation cuasing na+ release

• Extracellular k+ bind to thep ump, leading to dephshorylation

• The pump returns to the original conformation

• K+ is released from the pump

What are ion channels

Key drug targets

Secondary active transport

Cotransport - cation and chloride trasnporters

Examples of co transporter sym porters (3)

• na+/K+/cl-

• k+/cl-

• Na+/ neurotransmitter

Exampels of secondary active transport anti ports

• na+/ca2+

• Na+/H+

Similarities of primary and secondary active transport (5)

• against electrochemical gradient

• Carrier protein needed

  • Saturation

  • Sterespecificity

  • Competition

Differences in primary and econary active transport ñ

• priamry has direct energy input often ATP

• Secondary has indirect energy input required

What was teh first axon measure

Giant squid axon

Experimental methods to investigate ion channels

Patch clamp electrophysiology

How does patch clamp electrophysiology work CHECK

• use very fine glass ecletrode

• Fill with solution- -showed you could stick tups of surface of cll - shows ion movement when ion cahnnels were opne and closed