After reading this chapter I was confused about which cells had sodium pumps, which cells had voltage drops across their membrane, and which had voltage gated ligand channels. The giant axon of the squid is used when introducing this topic, and is the cell in which the values in table 11.1 come from. Because a nerve cell was used as the example, I wasn’t sure if the topics discussed are specific to a nerve cell or to cells in general. So I took to the internet.
First of all, all cells have sodium-potassium pumps. This makes sense, as all cells need to osmoregulate. According to Wikipedia, the sodium-potassium pump in a normal cell expends a third of the cell’s energy.
All cells do have a membrane potential, around that of the resting potential of a neuron. It is used to power some of the molecular devices in the membrane. However, not all cells can use it for signalling like neurons.
Voltage-gated ion channels are necessary in neurons, but again, according to Wikipedia, can be found in many kinds of cell. I had trouble finding examples other than muscle and neuronal cells, but I found one example. The Transient Receptor Potential Channels are voltage triggered. An example of a protein in this family is the capsaicin receptor, which responds to the chemicals which make chilli taste hot. Voltage gated ion channel are not found in every cell.
So everything that I found out here is pretty much what I expected. But I am glad I found out for sure, and I hope this helps confirm things for you too.
P.S. I can’t remember if I was taught this last year in BIPH2000, but in case I wasn’t, I thought I’d share: The research done on squid giant axons was not performed on the axons of a giant squid, but the giant axon of a regular sized squid. You probably already know this, but I didn’t realise this until it was pointed out to me.
Did you know that ion channels can also be ligand-gated. These are also present in neurons, but are present at the synapse. These channels are used to convert the chemical signal at the synaptic cleft into an electrical signal that can be sent down the neuron.
ReplyDeleteThere are also stretch-activated ion channels, these can sense mechanical stress. They are present in the hair cells in your ear.
This information was provided partly by my memory and partly by Wikipedia.
Good point there Heather, I had forgotten about the ligand-gated channels, and I like the point also about stretch-activated channels.
ReplyDeleteIn reference to your post Mitch, it certainly is quite difficult isn't it?
Certainly it is true that not every cell has voltage-gated activity associated with it (otherwise I think we could find ourselves in a bit of trouble with all of our cells actively working all the time)
Never realised though that the sodium-potassium channel took up a third of the energy.
Is there any more you can tell about the capsaican receptor? I find it quite interesting that such a receptor is voltage-gated based.
And finally, yes I did realise the point about the squid, probably likely due to the fact that the text never says giant squid, but just a giant axon from a squid.
I feel duped. I always imagined scientists fishing and fighting a GIANT squid...
ReplyDeleteI think most sensory receptors have some kind of voltage gated ion channels, as they need to respond to the thing they sense with an action potential. I think capsin is unusual because the thing it senses is detected through an ion channel also. I don't know how many sensory cells do this.
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