Voltage Clamp and current clamp

[JoshhChem213]

TL;DR

Determining ion selectivity for an ion channel

If i was conducting an experiment where i wanted to determine the ion selectivity of an ion channel that has a similar structure to voltage gated Na channel but is different in ion selectivity, would i use a voltage clamp or current clamp to figure this out. Also would i use a cell line or an animal model to transgenetically express gene?

 

[atyy]

To figure out ion selectivity, your main tool would be to vary which ions are present in the extracellular and intracellular solutions, and to measure whether current still flows when the ions are changed.

When the channel is voltage-dependent, like the voltage-gated sodium channel, voltage clamp is more typically used than current clamp to make a quantitative model of how the channel conductance changes when the voltage varies with time.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1392413/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6569590/

Ion channels are often studied by being expressed in frog eggs (Xenopus oocytes), but you can also express them in cell lines.
https://pubmed.ncbi.nlm.nih.gov/18998089/

 

[BillTre]

Expressing in frog eggs is very easy of you have the frog eggs available (which a lab that frequently does this kind of thing should have).
The frog eggs are so large you could almost microinject (with RNA) them by hand (without using a micromanipulator).

 

[JoshhChem213]

To figure out ion selectivity, your main tool would be to vary which ions are present in the extracellular and intracellular solutions, and to measure whether current still flows when the ions are changed.

When the channel is voltage-dependent, like the voltage-gated sodium channel, voltage clamp is more typically used than current clamp to make a quantitative model of how the channel conductance changes when the voltage varies with time.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1392413/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6569590/

Ion channels are often studied by being expressed in frog eggs (Xenopus oocytes), but you can also express them in cell lines.
https://pubmed.ncbi.nlm.nih.gov/18998089/

So my plan is to add channel blockers to determine ion selectivity. Would that be a time to use voltage gated as well? The voltage clamp will tell me if the channel is inactivated right?

 

[atyy]

So my plan is to add channel blockers to determine ion selectivity.

How would adding channel blockers will help you determine ion selectivity?

Would that be a time to use voltage gated as well? The voltage clamp will tell me if the channel is inactivated right?

In the case of the voltage-dependent sodium channel, you can use voltage clamp to ensure the channel is inactivated, because we know that depolarizing the channel will cause it first to open, then to inactivate.

However, you have to adjust the reasoning for other types of channel, since they probably have a different dependence of their various states on the voltage.