Lecture 3 Electrophysiolgoy Flashcards
What are ion channels?
Pore-forming proteins present in the plasma membrane of different cells
- allow passage of ions down their electrochemical gradient
- Help establish and control the voltage gradient across the plasma membrane
What are two important properties of ion channels?
- Gating
- the process of channel activation (opening), inactivation (prevent flow through open channel) and deactivation (closing)
- Permation/Selectivity
- Ion channel pores can allow over 10^6 ions to flow per second while at the same time selectively discriminate between different ions
In which 3 ways are ion channels classified?
- Ionic selectivity
- eg K+, Na+, Ca++, Cl-, nonselective
- Functional properties (activation trigger)
- voltage-gated
- ligand-gated
- mechanosensitive
- Molecular structure
- 2 transmembrane channels
- 2 transmembrane/2pore channels
- 4 transmembrane channels
- 6 transmembrane channels
- 24 transmembrane channels
- *** Anything greater than 24 requires 4 subunites
Define the cardiac action potential
A rapid and transient increase in the membrane potential that results in myocyte contraction
How is the cell membrane/AP similar to an electrical circuit?
Cm=
E=
gn =
gL =
Ip =
Cm= capacitance = lipid bilayer (structure that separates charges)
E= battery = electrochemical gradient (driving force)
gn = (t,v) = Non-linear electrical conductance, time (t) and voltage (v) dependent = gating property
gL = Linear electrical conductance, leak/ligand channels on in the background (independent of voltage)
Ip = Ionic pump

How is membrane potential calculated?
Membrane Potential = Vinterior - Vexterior
What is the Nernst potential of Ca++?
+150mV
Moved into cell during depolarization
What is the Nernst potential of Na+
+70mv
Into cell during depol
What is the nernst potential of Cl- ?
-30 to -65mv (moves into cell during repolarization and out of cell during depolarization)
What is the nernst potential of K+?
K+ is always higher intracellularly
Nernst potential (Erev) = -98mv
Moves out of cell during repol
In a single ion system, what controls the movement of ions across the cell membrane?
Nernst potetial:
AKA
- Reversal potential
- Equilibrium potential
What is Nernst potential?
A potential (for a single specific ion channel) at which there is no net flux of that particular ion across the cell membrane
What is the Nernst Equation?
E = (RT)/(zF) ln ([ion outside cell])/([ion inside cell])
or
E = 2.303 (RT)/(zF) log10 ([ion outside])/([ion inside])
E = nernst potential/membrane potential
R = the ideal gas constant (8.3145 J/molK)
T = temperature in Kelvin
F = faraday’s constant
z = ionic charge
How does Nernst equation change when dealing with a negatively charged ion? (eg Cl-)
Current is movement of POSITIVE charge so when dealing with a neg ion = outward current = invert the concentration relation
eg:
E = RT/zF ln ([Ion inside])/([ion outside])
What are the three types of Patch Clamp techniques?
- Cell-attached
- pull 1-2 ion channels into pipette
- Influence environment inside the pipette
- electrode acts as an ion channel
- Inside out
- Involves tearing piece of membrane to gain access to intracellular channels
- Ion channel regulated by intracellular ligands
- ability to manipulate intracellular enviornment
- Whole-cell
- Form giga-seal
- Interupt membrane inside the pipette
- Electrode is continuous with intracellular sol’n

Depolarization is the movement of _______ ions _______ the cell
Depolarization is the movement of positive ions into the cell
How does the membrane potential affect the movement of an ion across the cell membrane?
If Vm < Ek => K+ moves inward
If Vm > Ek => K+ moves outward
V = IR
V= I/G
I=VG
I = (Vm-E)G
What is the range of action for K+ channels in the heart?
-80mV to +40mV
Ek = -95mV
What happens to Na+ when the voltage is less than +70mV?
There will be an inward movement of Na+ (Na+ moves into cell)
ENa+= +70mV therefore when membrane current is less than +70, Na+ moves inward to increase membrane potential
What equation is used to measure Membrane Potential?
Goldman-hodgkin-katz (GHK) equation

Which 2 factors determing membrane potential (Em)?
- Concentraion gradients for K+, Na+ and Cl- across the membrane
- The relative permeability (electrical conductance / electrical gradient) of the membrane to each of these ions (regulated by ion channels)
What is channel gating?
Process of channel activation, inactivation, and deactivation
- Ligand-gated
- require ligand to bind
- Voltage gated
- respond to changes in membrane potential (Em)
The cardiac AP originates at the ______
Sinoatrial (SA) node
From the SA node, the AP travels:
From the SA node, the AP travels to the AV node, through the bundle of His, and into the right and left bundle branches before finally reaching the purkinje fibres
















