Mod 7 pt3

What is the physiological significance of cation channel selectivity in neurons?

Cation channel selectivity is critical for properly generating action potentials and synaptic responses, influencing whether a neuron depolarizes or hyperpolarizes.

How do neurotransmitter receptors like iGluRs and AChRs conduct Na+ to depolarize cells?

Despite being non-selective for Na+ vs K+, they conduct Na+ due to a greater driving force for Na+ influx at resting voltages, which is typically more than that for K+ efflux.

What factors affect the ion selectivity of non-selective cation channels?

The ion selectivity of non-selective channels is affected by the concentration gradient and the driving force of the ions, as well as the channel's permeability to different ions.

What experimental technique did A. and N. Takeuchi use to study synaptic AChR currents?

They used two-electrode voltage clamp to analyze the direction of synaptic potentials at different holding voltages in frogs.

What are cation channels less selective for Na+ or K+ compared to NaV and KV channels?

Examples include neurotransmitter receptors like nicotinic acetylcholine receptors and AMPA glutamate receptors.

How do non-selective cation channels generate excitatory postsynaptic potentials (EPSPs)?

They conduct depolarizing post-synaptic Na+ currents by having a greater driving force for Na+ influx than K+ efflux at resting voltages.

Why does ion selectivity matter for neurons at resting membrane potential (RMP)?

Na+ channels depolarize the cell, K+ channels hyperpolarize the cell, Ca2+ channels depolarize the cell and drive Ca2+ signaling, while Cl- channels can do either depending on the gradient.

What happens to the direction of current when voltage is considerably depolarized in nAChRs?

They conduct hyperpolarizing (outward) K+ currents due to a greater driving force for K+ than Na+.

What is the reversal potential (ERev)?

The voltage at which ion currents reverse from inward to outward, characterizing ion selectivity of different ion channels.

How did A. and N. Takeuchi study synaptic AChR currents?

They used two-electrode voltage clamp to analyze the direction of synaptic potentials at different holding voltages.

What can be inferred about a channel that has ERev occur at EK?

It is highly K+ selective.

What can be inferred about a channel that has ERev occur at ENa?

It is highly Na+ selective.

What does it mean for a channel to be non-selective?

The reversal potential will fall somewhere in between Na+ and K+ values, depending on the preference for each ion.

What is the significance of driving forces in ion channels like nAChRs?

The ion with the greater driving force will pass through the pore, influencing the net current.

What recent work was conducted in the Senatore lab regarding cation channel selectivity?

They characterized Deg/ENaC channels which are distinct from P-loop channels and tested their permeability to Na+, Li+, K+, and Cs+.

What drugs or conditions can activate Deg/ENaC channels?

They can be activated by various ligands including protons (pH), neuropeptides, and mechanical stimuli.

What was one finding regarding the permeability of the Deg/ENaC pore?

The pore is roughly 7x more permeable to Na+ than K+, equally permeable to Na+ and Li+, and 30x more permeable to Na+ than Cs+.

Which cation channel types tend to be highly selective for specific ions?

Nav, Kv, and Cav channels.

What is a characteristic of various other cation channel types compared to Nav, Kv, and Cav channels?

They do not discriminate ions as well, especially between monovalent cations Na+ and K+.

What types of cation channels are examples of non-selective channels?

nAChRs, iGluRs, TRP channels, and Deg/ENaCs.

What technique is often used to determine the reversal potentials in ion channels?

Voltage clamp technique.

How is the pore permeability assessed in ion channels like Deg/ENaC?

By exchanging external cations while keeping internal Na+ constant and recording the resulting currents.

What is the significance of knowing the driving force for Na+ and K+ in neurons?

It helps to understand how different ion channels influence neuronal excitability and signaling.

How is the permeability ratio to Na+ and K+ determined in experiments?

Using reversal potentials and comparing the currents produced by each ion.

What role do Ca2+ channels play in neurons?

Ca2+ channels depolarize the cell and are crucial for neurotransmitter release and signaling pathways.

What type of ion channel is primarily responsible for repolarizing the membrane after an action potential?

Voltage-gated K+ channels (Kv channels) are primarily responsible for repolarizing the membrane.

How do ligand-gated ion channels differ from voltage-gated ion channels?

Ligand-gated ion channels open in response to binding of a specific neurotransmitter, while voltage-gated channels open in response to changes in membrane potential.

What is meant by 'ion channel conductance'?

Ion channel conductance refers to the ability of an ion channel to allow ions to flow through it, typically measured in siemens.

What is the physiological effect of hyperpolarization in neurons?

Hyperpolarization makes the neuron less likely to fire an action potential, thereby inhibiting activity.