Inwardly rectifying K+ channel

[DoctaJay]

Am I the only one who is annoyed with this channel? Nothing about this channel is "inward". I would think that one of the PhD's in this country would figure out a way to rename it...ok, I just had to get this out of my system.

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[SemperJeff]

Am I the only one who is annoyed with this channel? Nothing about this channel is "inward". I would think that one of the PhD's in this country would figure out a way to rename it...ok, I just had to get this out of my system.

from Wikipedia:

These channels are termed inwardly rectifying - because they rectify current in the inward direction. This means that under equal but opposite electrochemical potentials, these channels will pass more inward current...

Thats the only explanation I've found for why its named that way. I think the only thing I saw in our notes was that it casues K eflux... right? I think its kinda sad how sometimes I find wikipedia more useful than my textbooks...

Wikipedia: Inward Rectifier K Channel

 

[DoctaJay]

I think your right semperjeff. I think I was only focusing on the "inward" part of the channel and not the "rectifying" part. Cool thanks for the clarification. I think it would be better though to just call it the K+ efflux channel.

 

[ZagDoc]

I think it would be better though to just call it the K+ efflux channel.

But that would MAKE SENSE! God forbid anything in science make sense!

 

[Sinfekl]

Now I see what you guys are talking about. I've always just thought of them as potassium leak channels.

A potassium "leak channel" generally refers to something else, although the terminology is vague enough to let it slip, I guess. K leak channels are important in maintaining resting membrane potential.

Why do I know that? Because instead of letting me get to the good stuff, my school essentially keeps in college for 4 months once I get here. Godamn cell physiology.

 

[SeventhSon]

allow me to provide an explanation that I believe is correct.

In order for an ion to pass through a channel, it must overcome some "activation energy" due to the electrostatics between it and and amino acids lining the inside of the ion channel.

It is not necessarily the case that the energy barrier going out --> in, is the same as in --> out.

The inwardly rectifying potassium channel has a lower activation energy going out-> in, than in-> out. However, under normal physiologic situations, K+ is an order of magnitude lower extracellularly than intracellularly, so by mass action, you have more potassium leaking outward than inward (in spite of the greater activation energy).

In a situation where extracellular potassium is elevated, mass action is no longer strong enough to cause a net leak of potassium outward, and due to the lower electrostatic energy of approach, potassium flows inward.

This makes teleological sense, as you would want your cells to quickly correct hyperkalemia ('inwardly rectifying'), if K is being elevated in the plasma.

 

[InternationlDoc]

from Wikipedia:


Thats the only explanation I've found for why its named that way. I think the only thing I saw in our notes was that it casues K eflux... right?

Wikipedia: Inward Rectifier K Channel

inward rectifying k+ channels is different than Delayed rectifier k+ channels which is different than 'leaky channels"

leaky k+ channels --> maintain membrane resting potential via constant leak. UNGATED

delayed rectifier ---> these are the ones that repolarize the heart cells

inward rectifying current --> these turn off during depolarization of heart so that you remian in plateu phase longer then start effluxing k+ out.
VOLTAGE SENSITIVE!

poster above me is absolutely correct in explaining the "inward rectifying" word mystery. its related to easier activation energy barrier...but there is just so much K+ intracellularly that I never bothered to care about it ..but you should

 

[alfonzarel]

allow me to provide an explanation that I believe is correct.

In order for an ion to pass through a channel, it must overcome some "activation energy" due to the electrostatics between it and and amino acids lining the inside of the ion channel.

It is not necessarily the case that the energy barrier going out --> in, is the same as in --> out.

The inwardly rectifying potassium channel has a lower activation energy going out-> in, than in-> out. However, under normal physiologic situations, K+ is an order of magnitude lower extracellularly than intracellularly, so by mass action, you have more potassium leaking outward than inward (in spite of the greater activation energy).

In a situation where extracellular potassium is elevated, mass action is no longer strong enough to cause a net leak of potassium outward, and due to the lower electrostatic energy of approach, potassium flows inward.

This makes teleological sense, as you would want your cells to quickly correct hyperkalemia ('inwardly rectifying'), if K is being elevated in the plasma.

I don't think so...

according to our physio class notes, K+ ALWAYS, ALWAYS flows OUT of a cell. if there actually WAS a K+ gradient that DID cause a reversal of flow from outside to inside, wouldn't that hyperkalemic state be so profound that you would indeed find yourself to be non-living? i believe that K+ will flow outward in order to always maintain the baseline potential inside the cell. if the cell is >-90 mV, the channels open and K+ flows out, repolarizing the cell. if the cell is <-90 mV, the channels close, reducing the hyperpolarization. internal potential regulation.

thus, the name: inward rectifier.

 

[SeventhSon]

I don't think so...

according to our physio class notes, K+ ALWAYS, ALWAYS flows OUT of a cell. if there actually WAS a K+ gradient that DID cause a reversal of flow from outside to inside, wouldn't that hyperkalemic state be so profound that you would indeed find yourself to be non-living? i believe that K+ will flow outward in order to always maintain the baseline potential inside the cell. if the cell is >-90 mV, the channels open and K+ flows out, repolarizing the cell. if the cell is <-90 mV, the channels close, reducing the hyperpolarization. internal potential regulation.

thus, the name: inward rectifier.

Firstly, K+ always flows in and out. Current describes the net flow of in and out of any given ion or collection of ions. Don't mean to sound prickish but this is actually important because it is the basis for establishment of the steady-state membrane potential. Statements like those found in your notes are meant to simplify things and present them at the conceptual level necessary to be a physician (also, many of those writing class notes have never taken physical chemistry)

Life would not be sustainable if there was a K+ concentration gradient that caused a net flow outward to inward, but it is not necessary for there to be a concentration gradient of K+ for inward flow, only that there is an electrochemical gradient. An electrochemical gradient/electrochemical potential has a concentration and an electrical component, and if the membrane potential is more negative than normal, electrostatics and thermal motion can tend to drag K+ in more than baseline, if the electrical component is large enough.

You are correct in observing that voltage-sensitive channels can aid in regulation of potassium flow (and ion flow in general). However, voltage-sensitive channels are not required at all for the regulation you speak of to take place... it is sufficient to have only electrostatics, random thermal motion, and the baseline permeability properties and ion channel populations of the membrane.

 

[UKMaltaMedStudent]

Hey, I came across this OLD thread in my frustration whilst learning about non-pacemaker action potentials.

I'm sorry guys but non of your answers explained this semantically silly phenomenon and so I did some more digging and came across this in Boron's Physiology;

"Although inward rectifying potassium channels pass current better in the inward than the outward direction, the membrane potential (Vm) is typically never more negative than Ek (equilibrium potential of potassium across the membrane). Thus,net inward K+ current does not occur physiologically. As a result, the activation of GIRK channels (G protein coupled inwardly rectifying potassium channel) hyperpolarizes cardiac cells by increasing K+ conductance or outward K+ current."

Your thoughts please ladies and gentlemen (if you can be bothered after 11 years hah!).