hyperkalemic periodic paralysis

[Kristen Chen]

To all of you with questions about hyperkalemic period paralysis.

Here's my take on hyperkalemia and it's relationship to paralysis: If the Na+ channels cannot inactivate, than as a result of the high concentration of Na+ outside of the cell, it will continue to flow into the cell, eliciting constant depolarizations.  At a certain point, the cell is just in this generally positive state such that any further depolarization/AP can't actually take off because there's no electrical gradient so the membrane can't be excited anymore, which means muscles can't be contracted which leads to muscle weakness. The condition is further aggravated by high extracellular potassium, which may be induced by eating a banana, because usually, K+ leaving the cell is what causes the cell to repolarize/hyperpolarize.  But if you have high extracellular potassium, you're going to have a smaller driving force, and consequently, potassium will tend to stay in the cell (at least more than normal) which further contributes to the depolarization of the cell.   

So I had originally posted on blackboard that inactivation of Na+ channels would lead to constant depolarization and constant muscle contraction so the muscle would be in this stiff state, but after reading up a little bit, I think that it's because the membrane potential can't be depolarized anymore so AP can't take off leading to muscle weakness (muscles can't contract). 

I attached an exert of the paper that Dr. Herrera has posted up under course documents-muscle channelopathies.  

If any of you guys can shed more light onto this topic, please do so by emailing me so I can post it!! I'm kind of speculating.