Lecture 5.3 - The electrophysiology of hypokalaemia and Hyperkalaemia

Normal K+ Levels

• K+ is a major intracellular cation, concentrated intracellularly through the Na+-K+ ATPase pump, which pumps 3 Na+ out and 2 K+ in.
• K+ ions maintain resting potential, allowing membranes to recover before the next action potential.
• Normal K+ levels in plasma range from 3.5-5.0 mmol/L.

Hypokalaemia (Low K+ Levels)

• Hypokalaemia occurs when there is less potassium in the plasma.
• It commonly occurs as a complication of diuretic therapy, such as in the treatment of hypertension, renal disease, and heart failure.
• Diuretics can eliminate potassium in the urine, leading to hypokalaemia.
• Electrophysiological consequences include:
  • Resting membrane hyperpolarization, as inward rectifier channels move more K+ outside, making the resting membrane potential (RMP) more negative.
  • Action potential (AP) duration prolongation.
  • Delayed repolarization (phase 3), as delayed rectifier channels move less K+ outside, prolonging the AP.
  • Predisposition to early after depolarization (EAD), which mediates arrhythmias.

Hyperkalaemia (High K+ Levels)

• Hyperkalaemia occurs when there is excess K+ outside the cell due to inward rectifier channels.
• It commonly occurs due to chronic or acute kidney failure.
• Electrophysiological consequences include:
  • Resting membrane potential becomes more positive.
  • AP duration shortening.
  • Slow conduction velocity, as phase 3 happens quickly, leading to inactivation of Na+ channels.
  • Predisposition to heart block, asystole, and re-entry currents.