Ion Channel Receptors Flashcards
(40 cards)
What are Ion Channel Receptors?
Type of Membrane bound protein that allows the selective passage of ions across the cell membrane in response to stimulus following the electrochemical potential gradients
What is a malfunction of Ion channel, either gain or loss of function called?
Channelopathies
What are the differences between Ion channel receptors and other membrane receptors?
- Mechanism of Action: Direct ion flow through a channel vs Indirect signalling via second messengers
- Response time: Fast (milliseconds) vs Slower (seconds to minutes)
- Biological role: Rapid, synaptic transmission, muscle contractions vs Long term modulation of cell function
What are the differences in mechanism of action of Ion channels vs others?
Direct Passage of Ion flow through a channel vs indirect signalling via secondary messengers
What are the differcnes in Response time between ion channels and others?
Millisseconds vs Minutes/seconds
What are the differcens in Biological role between ion channels and others>?
Rapid Synaptic Transmissions, muscle contractions vs Long term modulation of cell function
Where do Ion channel receptors occur in?
Excitable cells: Neurons -neuronal signalling (action potential propagation)
Muscle Cells - muscular contractions
What is an electrochemical gradient?
Conductance, a comination of 2 forces thgat drive hte movement of ions across a mebrane
comprising of
1. Chemical gradient
2. electrical gradient
What charge is usually the internal of the cell
Negative
What is the equilibrium potential of Na+?
+60mV
What is the equilibrium potential of K+?
-80mV
What is Resting potential?
the membrane potential difference at which there is no net current and no net solute flow
Where does resting potential come from?
Determined by the balance of equilibrium potentials for K+ and Na+
Represents an average effect of all leaky K+ an Na+ channels
if only K+ leaky channels were present, the potential would rapidly reach -80mV
if only na+ leaky channels present, the potential would rapidly reach +60mV
What is the resting potential and why is that the value?
The resting potential is -70mV , which is alot closer to K+ (-80), insetad of the supposed average fo both potential (-10)
This is becasue K+ channels outnumber Na+ channel 14:1
Thus the resting potential is far more influenced by K+ leaky channels than Na+
What is an action potential?
A transient short lasting reversal in membrane potential triggering a wave of electrical activity that propgates across the membrane
What are the steps of an action potential formation?
- Resting Potential (-70mV) - Na+/K+ channels are closed, maintained by Na+/K+ pump
- Stimulus and depoalrisation towards threshhold - A stimulus from sensory cells or another neuron causes partial depolarisation
- if threshhold potenial of -55mV is reached, action potential is triggered - Rapid Depoalrisation
Na+ channeles open, allowing Na influx into the cell, making membrane more positive (+30mV) - Peak and Repolarisation- At the peak of action potential, Na+ channels inactiavte, K+channels open, K+ efflux, restoring negativity and repoalrisation
- Hyperpolarisation and refractory period
Excess K+ efflux causes hyperpoalrisation (-80mV)
Neuron enters refractory period where it cannot fire another action potential (absolute) or require a stronger than usual stimulus (relative) - Restoration of resting potential
K+ channels close, Na+/K+ reset resting potential -70mV
What are the 3 structural features of Ion channels?
- Selectivity filter - determine which ions can pass throufgh
- Gating Mechanism - Control opening and closing in response to external stimuli, regulating membran permeability
- Activation sensors - Controlled by elctrical chemical of mechancial stimuli
What are the characteristics of Ion Channels?
- Membran spanning proteins with water filled pores
- Ion Selectivity
- Rate and direction driven by electrochemical gradient
- Gating mechanism
- Activity is regualted by phosphorylation
What are the 4 types of ion channel receptors?
- Leakage
- Ligand
- Voltage
- Signal
What are leakage channels?
- Always open, allowing passive ion movement down the concentration gradient
- K+ and Na+ leaky channels
-K+ efflux maintains neuron’s negative resting potential (-70mV)
Na+ influx partially ofsets K+ movement - prevents excessive hyperpolarisation
What are voltage gated ion channels?
Open or close in response to changes in membrane potential
selective for certain ions
Found in neurons, muscles cardiac cells
Axons- responsible for action potential generation and propoagation
What are Ligand gated ion channels?
Open in response to ligand (chemical) binding
Allow selective ion flow
What are Signal Gated Channels?
Open and close in response to intracellular signalling molecules, not direct ligand binding
linked ot GPCR
What is the purpose of Na+ voltage gated channels?
Open for Depolarisation, initaiting action potential
