Hyperkalemia is a serious metabolic state where there is elevated plasma (serum)
ID: 96778 • Letter: H
Question
Hyperkalemia is a serious metabolic state where there is elevated plasma (serum) potassium (K+ ) leading to high extracellular K+ levels. Symptoms include tingling sensations, muscle weakness and paralysis, and potentially fatal heart arrhythmia. The salt, KCl, has been used in lethal injections and induces hyperkalemia. Explain why hyperkalemia makes muscle contraction less likely (hence weakness)? In cases of hyperkalemia, does the resting membrane potential becoming more or less negative? How does that affect generation of an action potential? In order to figure this out, isolate the effect of the K+ gradient on RMP and AP normally, and deduce how elevated K+ changes the RMP relative to the threshold potential.
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Explanation / Answer
In hyperkalemia, the concentration of extracellular K+ increases to high levels preventing the passive flow of K+ from inside the cell to outside. It causes depolarization of membrane (means more positive than it is at resting potential). Resting membrane potential decreases to nearly threshold value (less negative). It increases Excitability of muscle. As the value of resting potential decreases, the amplitude of action potential also decreases than normal range.
Normally, K+ is present in high concentrations inside the cell and there is low concentration of K+ outside the cell. The resting membrane potential mainly depends on movement of K+ through potassium channels across the membrane. So, K+ will move from inside towards outside. With every K+ passing out, the inside of cell loses one positive charge. Due to this movement, there develops more positive charge outside and a negative charge develops inside.
Now if there is high K+ outside, there will be no movement of K+ from intracellular fluid to extracellular fluid because already extracellular fluid has more positive charge. In this way the cell will get depolarized. The extent of depolarization will depend on how much K+ is more outside than normal conditions.
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