Basic: Na transport?

[Pathinterpreter]

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Hi. I was reviewing the questions in BRS physiology 1st edition and it says Na inward current in depolarization is a simple diffusion. I think this is wrong because Na obviously is an ion, so it is lipophobic, so it needs an integral protein (carrier mediated). Can somebody tell me how it is?
Thank you.


"Never let anybody take away your dreams"

 

[DarlynVMD]

This statement is correct and not incorrect. Remember that the Na/K ATPase establishes the concentration gradient across the cell membrane (i.e., low intracellular [Na], while maintaining a high extracellular [Na] and the opposite for potassium.) So since there is a high [Na] extracellularly compared to intracellularly, when the activation gates open during depolarization, Na is going to flow passively (i.e., simple diffusion) from a region of high concentration to region of low concentration.

 

[Hallm_7]

The inside of sodium channels are lined with hydrophilic amino acids in several alpha helices, so Na ions can flow through unimpeded when they are opened. The Na channels you speak of are voltage gated and only open when there is a slight depolarization caused by synaptic Na channels opened by ligand (ACh).

When you read "ion channel" think diffusion and going down the concentraton gradient. When you read "ion pump" think active transport and going up the concentration gradient.

 

[Hallm_7]

double post

 

[Miami_med]

Na+ in is simple diffusion. Na+ out is active transport via the Na+/K+ pump.

Remember that the cell is both polarized and Na+ has a significant concentration gradient across the cell before the AP. Any permeability in the membrane to NA+ will quickly be taken advantage of, as every force wants to push Na+ into the cell.

 

[Rugby MD]

Na+ in is FACILITATED diffusion. it has a channel and this therefore facilitated. if it just floated through the pm, which it doesn't, then it would be simple diffusion. steroid hormones are diffuse by simple diffusion.
brain melting as I type.
rugby

 

[drss]

I agree with darylnVMD...if u guys remember at peak of AP all channels(max fast Na+ are open but Na+ AP at equilbrium so no net force and its signal to K+ to repolarize!

 

[SoCuteMD]

Na+ in is FACILITATED diffusion. it has a channel and this therefore facilitated. if it just floated through the pm, which it doesn't, then it would be simple diffusion. steroid hormones are diffuse by simple diffusion.
brain melting as I type.
rugby

ding ding ding! We have a winner!

Darlyn VMD's statements about concentration gradient are also correct.

 

[SeventhSon]

it also cannot be simple diffusion because there is an electric potential driving the motion of Na+. I believe simple diffusion refers only to random thermal motion of molecules, not a combination of random thermal motion and an electrostatic force from a potential difference.

edit: i looked at some reference books and got different answers. Damn biology books lack precision so it's impossible to tell what the exact definition is.

 

[ayanjoe]

Don't bother guys ! this is Low-Yield material anyway !