Number of Ion Channel

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RedBull
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Number of Ion Channel

Do anyone know how many ion channels are there in the world?

Fraser Moss
Fraser Moss's picture
Wow! You could ask "how long

Wow! You could ask "how long is a piece of string?" and expect a similar kind of answer. Although as each different genome is sequenced, we will be able to predict the number of different channels that exist, this is still going to take a while to be able to dinitively answer this question. Also, one cannot predict 100% confidence the existence of a particular hyothetical channel from the genome without functional proof, because not all the predicted ion channel subunits may actually be expressed.

You would have to break down the known channels and predicted channels into their classes to attempt this. Also, because many channels are formed from heteromultimers of different subunits, which each can have several splice variants or undergo other post-translational modifications, the number of possible channels in just one class is huge.

Here's just a taster of what's out there in 1 class - (and the numbers I quote are just in Human)

1. Ligand-Gated Ion Channels

a) the cys-loop superfamily
nicotinic receptors (10 alpha proteins, 4 beta, 1 gamma, 1 delta and 1 epsilon)
5-HT3 receptors (5 subunits, A-E)
GABA-A and GABA-C receptors (6 alphas, 3 betas, 1 delta, 1 epsilon, 2 gammas, 1 pi, ρ1-3 subunits, θ subunit)
glycine receptors (3 alpha, 1 beta)
some glutamate , histamine and serotonin activated anionic channels

b) ATP gated channels - P2X 1-7

c) Glutamate activated cationic channels - GluR 1-7, NR1-3 (4 splice variants of NR2), KA1 & 2

Then there are also the voltage gated ion channels, the tension gated ion channels etc etc.

I could spend a week writing this post.

Good resources to answer your question are.

http://www.ebi.ac.uk/compneur-srv/LGICdb/LGICdb.php

http://vkcdb.biology.ualberta.ca/

http://www.iuphar-db.org/iuphar-ic/aboutICC.html

http://www.iuphar-db.org/iuphar-rd/

If you ever get an definitive absolute number please post again and let us all know!

RedBull
RedBull's picture
Well....

Well....
My colleague say 5

as shown below:

K+ leak
Ca- ion
Na- ion
K- ion
Na+/K+ pump

Do any of you agree?

RedBull
RedBull's picture
frasermoss wrote:Wow! You

frasermoss wrote:

Wow! You could ask "how long is a piece of string?" and expect a similar kind of answer. Although as each different genome is sequenced, we will be able to predict the number of different channels that exist, this is still going to take a while to be able to dinitively answer this question. Also, one cannot predict 100% confidence the existence of a particular hyothetical channel from the genome without functional proof, because not all the predicted ion channel subunits may actually be expressed.

You would have to break down the known channels and predicted channels into their classes to attempt this. Also, because many channels are formed from heteromultimers of different subunits, which each can have several splice variants or undergo other post-translational modifications, the number of possible channels in just one class is huge.

Here's just a taster of what's out there in 1 class - (and the numbers I quote are just in Human)

1. Ligand-Gated Ion Channels

a) the cys-loop superfamily
nicotinic receptors (10 alpha proteins, 4 beta, 1 gamma, 1 delta and 1 epsilon)
5-HT3 receptors (5 subunits, A-E)
GABA-A and GABA-C receptors (6 alphas, 3 betas, 1 delta, 1 epsilon, 2 gammas, 1 pi, ρ1-3 subunits, θ subunit)
glycine receptors (3 alpha, 1 beta)
some glutamate , histamine and serotonin activated anionic channels

b) ATP gated channels - P2X 1-7

c) Glutamate activated cationic channels - GluR 1-7, NR1-3 (4 splice variants of NR2), KA1 & 2

Then there are also the voltage gated ion channels, the tension gated ion channels etc etc.

I could spend a week writing this post.

Good resources to answer your question are.

http://www.ebi.ac.uk/compneur-srv/LGICdb/LGICdb.php

http://vkcdb.biology.ualberta.ca/

http://www.iuphar-db.org/iuphar-ic/aboutICC.html

http://www.iuphar-db.org/iuphar-rd/

If you ever get an definitive absolute number please post again and let us all know!

Very good!

You had given a very detailed reply.

Really thanks to you.

Fraser Moss
Fraser Moss's picture
Quote:Well....

Quote:

Well....
My colleague say 5

as shown below:

K+ leak
Ca- ion
Na- ion
K- ion
Na+/K+ pump

Do any of you agree?

No I dont agree. That is a very crude way to classify all the chanel types out there and it does not cover all the possibilities.

Also The Na+/K+ pump is not an ion channel in the true definition of the word, but an active transporter. That is the ions are moved against their concentration gradient by the pump, and the energy needed to drive the process is supplied by the hydrolysis of an ATP molecule to ADP.

Ion channels always gate the movement of ions in the direction of their electrochemical gradient. No additional energy is required to drive the process.

If I were to try to start to classify all the channels out there according to your scheme then I could list:

Mechanosensitive channels
K+ leak channels
G-protein coupled inward rectifying potassium channels
Calcium-activated K+ channels
Voltage gated K+ channels
Voltage gated Na+ channels
Voltage gated Ca2+ channels
Voltage gated Cl- channels (ClC)
Ligand gated cation channels
Ligand gated anion channels
Ca2+ activated Cl- channels

I'm sure I've missed some but I hope you get the idea.