Lecture 5.3 - Hypokalaemia and Hyperkalaemia PDF

Normal K+ levels: ◦Major intracellular cation and is concentrated intracellularly: Na+-K+ ATPase pump (3 Na+ out, 2 K+ in) ‣ Potassium ions maintain resting potential to allow membranes to recover before next action potential ◦Normal K+ levels in plasma - 3.5-5.0...

Normal K+ levels: ◦Major intracellular cation and is concentrated intracellularly: Na+-K+ ATPase pump (3 Na+ out, 2 K+ in) ‣ Potassium ions maintain resting potential to allow membranes to recover before next action potential ◦Normal K+ levels in plasma - 3.5-5.0 mmol/L ◦Low levels of plasma K+ - hypokalaemia ◦High levels of plasma K+ - hyperkalaemia Hypokalaemia: ◦Less potassium in the plasma ◦Most commonly occur as a complication of diuretic therapy (which is normally used to treat hypertension, renal disease and heart failure) ‣ Diuretics can eliminate potassium in the urine, so patients can develop hypokalaemia ◦Electrophysiological consequence - contractile cells: ‣ Resting membrane hyperpolarisation - inward rectifier channels move more K+ outside, losing positive charge and RMP becomes more negative ‣ AP duration prolongation ‣ Delayed repolarisation (phase 3) - Delayed rectifier channels move less K+ outside, so Action potential prolongs ‣ Predisposes too early after depolarisation (EAD) - sodium-potassium pump affects the activity of sodium-calcium exchangers, so early after depolarisation takes place ‣ EAD mediated arrhythmias Hyperkalaemia: ◦Excess K+ outside the cell due to inward rectifier channels ◦Most commonly occur due to chronic/acute kidney failure ◦Electrophysiological consequence: ◦Resting membrane potential more positive ◦AP duration shortening ◦Slow conduction velocity because phase 3 happens quickly, so Na+ channels become inactivated ◦Can lead to heart block, asystole and re-entry currents