ZIMA Lecture 3: Channel Structure and Function Flashcards
Ion channels are transporters that use _________
Ion channels have ________ pores that can open and close ______
Ion selectivity (selective filter) means ______
Ion channels are/are not continously open. They are ____ between open and closed states. With prolonged stimulation, most channels_____
Ion channels are transporters that use electrochemical potential
Ion channels have narrow, highly selective pores that can open and close rapidly
Ion selectivity (selective filter) means permitting to pass specific ions (Na or K or Ca or Cl)
Ion channels are NOT continously open. Instead, they are gated between open and closed states. Moreover, with prolonged stimulation, most channels go into a closed “inactivated” state
What are the three major types of ion channels?
Channel gating is controlled either by:
1. voltage
- ligand
- mechanical stress
At rest, the cell membrane is freely permeable to which ion?
What creates the negative membrane potential?
When does the net effux of that ion stop?
What does ‘Nernst potential’ for that ion mean?
At rest the cell is freely permeable to K+
K+ leak from the cell creates a negative membrane potential
The net efflux of K+ halts when the membrane potential reaches a value at which electrical driving force on K+ exactly balance the effect of its concentration gradient.
K+ equilibrium potential (K Nernst potential): the membrane potential at which there is no net flux of K+
What are the three things that determine Nernst Potential?
What are the two equations for Nernst Potential?
Nernst potential is determined by:
- Ion concentrations
- Temperature
- Ion valence
Note: only a very small numner of ions must move across the membrane to set up membrane potential. It takes just 10^-12 M of potassium per square centimeter to develop membrane potential of -100 mV
Explain the role of K leak vs Na/K ATPase pump in the development of the resting membrane potential
Because the Na/K pump is electrogenic, it can also contribute to the RMP. However, this contribution is significantly smaller (around 10%) compared to K+ leak channels (90%)
Explain the structure of ion channels:
Negative charged amino acids concentrated at the cytosolic entrance of the pore attract cations and repel anions, making the channel cation-selective
K+ ions must lose all of its bound water to enter filter
The channel gating (a transition between closed and open state) involved the movement of the helices in the membrane so they either obstruct (the closed state) or free (open state) the path for ions
What are the three voltage gated cation channels?
What are the three excitatory transmitter gated ion channels?
What are the two inhibitory transmitter gated ion channels?
Voltage gated cation channels: voltage gated Na channels, voltage gated K channels, voltage gated Ca channels
Excitatory: ACh gated cation channels, Glutamate gated Ca channels, serotonin gated cation channel
Inhibitory: GABA gated Cl- channels, Glycine gated Cl- channels
The main task of neurons is to ____, ____, _____
The signal is always the same: ______
How can neurons communicated with each other?
The main task of nerusons is to receive, conduct, and transmit signals.
The signal is always the same: the action potential
By changing firing a frequency of action potentials, neurons communicate with each other
Na+ channels are activated by?
Na+ channel activation increases w/______
The positive feedback is counterbalanced by what two things?
Na+ channels are activated by membrane depolarization
Na+ channel activation increases with depolarization (positive feedback)
The positive feedback is counterbalanced by 1) Na+ channel inactivation and 2) opening voltage-activated K+ channels
Explain the ball and chain model of inactivation
What is responsible fo action potential propogation?
Na+ channel inactivation is responsible for unidirectional propogation of the action potential (when AP has reached the axon terminal it will not go back to the soma)
What happens if you induce an AP in the middle?
The AP will carry on in both directions
What are the two major components of total membrane current?
What does membrane depolarization lead to?
Total membrane current has two major components:
- Initial Inward Current (Na+)
- Late Outward Current (K+)
Membrane depolarization leads to:
- Activation of Na+ channels
- Subsequent Inactivation of Na+ channels
- Activation of K+ channels (with a delay)
Explain the myelination of neurons
The axons of many vertebrate neurons are insulated by myelin sheath, which GREATLY INCREASES the rate at which an axon can conduct an AP.
Myelin produced by Schwann Cells (PNS)
Oligodendrocytes (CNS)
Myelin sheath interrupted at nodes of Ranvier (where the sodium channels are concentrated)
AP propogates along an axon quickly by jumping from node to node (saltatory conduction)
Explain the patch-clamp technique.
Whole cell currnet is the summation of all single channel currnets in the cell membrane.
The patch clamp technique allows studying ion current through a single molecule of a channel protein.
All single channels open in an all or nothing fashion
Neuronal signals are transmitted from cell to cell at specialized sites known as _____.
Transmission of signals is usually indirect: it involves what two things?
Neuronal signals are transmitted from cell to cell at specialized sites known as synpases.
Transmission of signals is usually indirect.
It involves 1) neurotransmitter and 2) transmitter-gated ion channels
Explain transmitter gated ion channels
Transmitter gated ion channels open transiently in reponse to the binding of neurotransmitters, thereby producting a brief increase in ion conductance.
Transmitter gated ion channels produce local changes of membrane potential, that are graded according to the amount of neurotransmitters and how long it persists at the synpases
Excitatory vs Inhibitory NTs
Excitatory NTs depolarize the post-synaptic neuron (open Na+ channels)
Inhibitory NTs hyperpolarize the post-synaptic neuron (open K+ of Cl- channels)
Explain the ACh receptor
The ACh receptor (nicotonic) is opened upon the release of ACh from the nerve terminal at the neuromuscular junction (activation of skeletal muscle contraction)
Two binding sites for ACh
This was the first ion channel to be cloned, sequences, and characterized in terms of single channel properties
Explain the cascade of events at the Neuromuscular Junction
- Opening of voltage gated Ca++ channels in the nerve terminal membrane causes a release of ACh into the synaptic cleft
- Activation of ACh receptors in the muscle cell causes a local membrane depolarization
- Activation of voltage gated Na+ channels causes the action potential generation
- Membrane depolarization activates voltage gated Ca++ chjannels in the T-tubules
- This causes Ca release from the sarcoplasmic reticulum and muscle contraction
RMP of the nerve cell is a direct consequence of:
High K+ channel permeability/ K+ leak
Which agent could paralyze/stop skeletal muscle activity?
Nicotinic Receptor Blocking Agent
REMEMBER: Nicotinic is skeletal
Muscarinic is smooth
