Ion Channels and Electrophysiology

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Questions and Answers

What is the effect of Ohm's Law on current in an electrical circuit?

Current is directly proportional to voltage and inversely proportional to resistance. (correct)

Current is inversely proportional to voltage.

Current is equal to resistance multiplied by voltage.

Current is directly proportional to resistance.

In the context of ion substitution, which ion can replace Na+ in the example given?

Choline+ (correct)

K+

Ca2+

Li+

What characterizes the 'inward rectifier' phenomenon in ion channels?

They pass K+ better into the cell than out. (correct)

They only allow Na+ to pass through the channel.

They completely block any ion movement.

They allow K+ to move out of the cell more easily.

What is typically ignored when measuring the resistance of an ionic solution in a pipette?

The resistance of the solution. Signup and view all the answers

What happens to the neurone during the 'holding' phase in the experiment?

It is held at a desired potential. Signup and view all the answers

What is the role of Na+/K+ ATPase in maintaining ionic balance?

It maintains a non-equilibrium state of these ions. Signup and view all the answers

What is the typical resistance of a seal formed in a neuronal unit?

GigaOhms Signup and view all the answers

What does rectification in ion currents refer to?

The phenomenon where current flows predominantly in one direction. Signup and view all the answers

What is the primary role of ion channels in neurons?

To facilitate the movement of ions across the membrane Signup and view all the answers

Which equation is used to understand the equilibrium potential of ions across a membrane?

Nernst equation Signup and view all the answers

What distinguishes ligand-gated ion channels from voltage-gated ion channels?

They are activated by the binding of neurotransmitters Signup and view all the answers

What is the effect of the Na+/K+ ATPase on ion concentration across the membrane?

It maintains unequal concentrations of Na+ and K+ Signup and view all the answers

During the generation of an action potential, what primarily causes the depolarization phase?

Na+ ions entering the cell Signup and view all the answers

What is the resting membrane potential typically around in nerve cells?

-60 mV Signup and view all the answers

What primarily shapes the behavior of a neuron when it is at rest?

The combination of ion currents through ion channels Signup and view all the answers

What type of channels are described as “leak” channels?

Channels that are always open and help maintain resting membrane potential Signup and view all the answers

What is the unit of conductance commonly used for neuronal recordings?

Siemens Signup and view all the answers

How does the reverse of resistance relate to ion channels?

It measures conductance. Signup and view all the answers

Which type of experimental setup is used to study individual ion channels?

Patch clamp Signup and view all the answers

During which mode can you inject current into a cell while measuring its response?

Whole cell mode Signup and view all the answers

What type of currents do we measure when using the classic two-electrode voltage clamp?

Macro currents from large populations Signup and view all the answers

What happens when extracellular solutions' ion concentrations are manipulated during experiments?

It alters ion current measurements. Signup and view all the answers

What was a notable use for Xenopus oocytes in electrophysiological studies?

They are easy for expressing genetic constructs. Signup and view all the answers

What type of currents does the range from macro currents to pico-currents in electrophysiology cover?

Activity of large populations to individual ion channels Signup and view all the answers

What is the primary reason a smaller Na+ ion cannot pass through a K+ pore?

The size of the ion is incompatible with interactions in the pore. Signup and view all the answers

Which type of ion channels is always open without a specific stimulus?

Leak channels Signup and view all the answers

What primarily regulates inward rectifier K+ channels?

Intracellular signaling mechanisms Signup and view all the answers

What characterizes the selectivity of ion channels?

Ions must interact with specific residues in the pore. Signup and view all the answers

Why might non-selective cation channels conduct more than one type of ion?

Their design allows multiple ions to fit. Signup and view all the answers

What factors can influence the activity of potassium channels?

pH, temperature, and extracellular signaling molecules Signup and view all the answers

What is a key function of leak potassium channels?

They establish a resting membrane potential. Signup and view all the answers

How do gated channels differ from leak channels?

Gated channels respond to specific stimuli. Signup and view all the answers

What causes the resting membrane potential (RMP) to be negative inside the cell?

The efflux of K+ ions following their concentration gradient Signup and view all the answers

What happens when the electrical field is strong enough to completely balance out the chemical gradient?

The system achieves equilibrium Signup and view all the answers

What represents the potential at which the net flux of a particular ion is zero?

Equilibrium (Reversal) potential Signup and view all the answers

Which of the following best describes what happens to K+ ions at resting membrane potential?

They leak out of the cell through leaky channels Signup and view all the answers

What is the chemical driving force primarily related to in neurons?

Concentration gradients of ions Signup and view all the answers

At equilibrium potential, what happens to the electric and chemical driving forces?

They are equal Signup and view all the answers

Why is potassium often referred to as having 'leaky' channels in the context of resting membrane potential?

K+ ions can easily pass through non-gated channels Signup and view all the answers

What is the impact of a stronger electrical gradient on K+ ions as they exit the cell?

It leads to a reduction in their exit rate Signup and view all the answers

Which ion is primarily associated with the establishment of the resting membrane potential in cells?

K+ Signup and view all the answers

What results from the simultaneous action of electrical and chemical gradients on K+ ions?

A net efflux of K+ ions occurs Signup and view all the answers

Study Notes

Introduction

Ion Channels are responsible for the maintenance of the resting membrane potential and the generation of action potentials
The function of ion channels can be studied using electrophysiology and biophysical techniques

What are ion channels and how we study them?

Ions cross plasma membranes via ion channels
Ion channels are present in all cells
Electrical activity of a neurone is determined by the flow of ions via ion channels
I/V plots can be used to study the relationship between membrane potential and current flow through ion channels
Nernst and Goldman equations are used to calculate the equilibrium potential of ions
The resting membrane potential (RMP) is generated by the steady exit of K+ ions through specialized K+ channels

The Na/K ATPase

The Na/K ATPase pumps 3 Na+ ions out of the cell for every 2 K+ ions pumped in
The Na/K ATPase is mildly electrogenic, but does not contribute significantly to the generation of resting membrane potential

Generation of Resting Membrane Potential

The resting membrane potential is generated by the efflux of K+ ions through leak channels
Leak channels are open all the time and have moderate conductance
K+ ions exit the cell following their concentration gradient, resulting in a negative membrane potential

The Equilibrium Potential

The equilibrium potential (reversal potential) is the membrane potential at which the electrical driving force and chemical driving force are equal
At the equilibrium potential, the net flux of the ion is zero
The equilibrium potential impacts neuronal excitability, affecting the ability to generate action potentials

How we study Ion Channels Using Electrophysiology

Electrophysiology allows study of ion channel activity at different scales
Whole-cell patch clamp records currents from a single neuron
Cell-attached recording records action potential frequency and patterns
Voltage clamp allows controlling membrane potential and measuring current flow
Patch clamp isolates currents from small groups of channels
Extracellular recording studies action potentials from large groups of neurons

Conductance

The slope of the IV plot can be used to calculate channel conductance
Conductance is the inverse of resistance
Conductance is measured in Siemens

Rectification

"Inward rectifiers" pass K+ ions better into the cell than out of the cell
This phenomenon is essential for the function of ion channels
The mechanism of rectification is not completely understood

Ion Selectivity

The selectivity of ion channels depends on the size and charge of the ions, and the amino acid residues lining the pore
K+ channels are selective for K+ ions, while Na+ ions cannot pass through the pore
Some ion channels are non-selective, conducting multiple ions

Types of Ion Channels

"Leak" channels are open all the time, and have moderate conductance
"Gated" channels open and close in response to a specific stimulus
The activity of leak channels can change on a slow time scale
Gated channels are responsible for fast electrical events in neurons

Potassium Channels

Two main classes of K+ channels are responsible for resting membrane potential:
- Two-pore domain (K2P ) channels
- Four-transmembrane domain channels
K2P channels are regulated by intracellular signalling mechanisms and are sensitive to various factors like pH and temperature
Four-transmembrane domain channels are regulated by extracellular signalling molecules and are responsive to various environmental stimuli
Potassium channels are essential for maintaining the resting membrane potential and regulating neuronal excitability

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Description

Explore the crucial role of ion channels in maintaining the resting membrane potential and generating action potentials in neurons. This quiz also delves into the study of ion channels using electrophysiology, including calculations involving Nernst and Goldman equations as well as the function of the Na/K ATPase.