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melRN80
09-22-2009, 12:51 PM
if one were to change the extracellular concentration of sodium why would the effect on the membrane potential not be as significant such as when the extracellular concentration of potassium is changed?

eldano
11-10-2009, 03:26 PM
Because the main ion who controls the Resting membrane potential are the K+ therefore and increase in Na+ would not have much of an effect in the resting membrane potential. This is true because most Na+ channels are impermeable to Na+ or remaing close and depend in changes in membrane potential to open. On the other hand, the potassium channels, which are sometimes refer as leaky or ungated channels, constantly permit the diffusion of K+ ions from an area of greater concentration( intracellular space) to and area of lower contration (extracellular). Or to simplified things potassium channels are always open and K goes to the outside.
So, an increase in Potassium rather than sodium, will change the concentration differences between the intracellular space and the extracellular space. If you INCREASE the concentration of potassium in the extracellular space the concentration differences would be lower therefore the membrane potential would be more positive or partially depolarize, OR LESS NEGATIVE. Now if you REDUCE the concentration of K+ in the extracellular membrane you will DECREASE the concentration differences across the membrane and the membrane potential will be more negative (i.e. -90 to -100).
Applying that to a clinical scenario you can see why hyperkalemia and hypokalemia would have a bigger consequence in tissues like muscle,heart and neurons, which required a certain resting potential in order to function properly.
Now the sign and symptoms of hyperkalemia and hypokalemia can be post by some else cause I don't want to have all the fun....

statiastudent347
05-24-2010, 11:32 AM
b/c at rest when the membrane is resting there is only ungated K+ channels so if K+ is affect the cell RESTING MEMBRANE will be affected







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