Overview

Top Half — Factors That SHIFT K⁺ INTO the Cell (→ Lower serum K⁺)

1. Alkalosis → via Reversible H⁺/K⁺ Exchanger

• In alkalosis, the blood has too little H⁺.
• To compensate, cells release H⁺ into the extracellular space in exchange for taking K⁺ into the cell.
• This lowers serum K⁺, which is why alkalosis frequently causes hypokalemia.

2. β-Agonists and Insulin → via Na⁺/K⁺-ATPase

• Both β₂-adrenergic agonists (e.g., salbutamol/albuterol) and insulin stimulate the Na⁺/K⁺-ATPase pump.
• This pump moves 2 K⁺ into the cell and 3 Na⁺ out, actively driving K⁺ intracellularly.
• Their effects are additive — both can be exploited clinically to treat acute hyperkalemia.

Bottom Half — Factors That SHIFT K⁺ OUT of the Cell (→ Raise serum K⁺)

1. Digoxin, β-Blockers, Hypoinsulinemia → via Na⁺/K⁺-ATPase (Inhibition)

• Digoxin directly inhibits Na⁺/K⁺-ATPase → K⁺ can no longer be pumped into cells → serum K⁺ rises.
• β-Blockers block the β₂ receptor, preventing catecholamine-driven K⁺ uptake.
• Hypoinsulinemia (low insulin, e.g., in diabetic ketoacidosis) removes the insulin stimulus on the pump.

2. Acidosis → via Reversible H⁺/K⁺ Exchanger

• In acidosis, excess H⁺ enters the cell to be buffered.
• In exchange, K⁺ is expelled out of the cell into the extracellular fluid.
• This is why acidosis causes hyperkalemia (and vice versa — correcting acidosis shifts K⁺ back in and can unmask hypokalemia).

3. Succinylcholine → via Nicotinic Acetylcholine Receptor (nAChR)

• Succinylcholine (a depolarizing neuromuscular blocker) persistently activates nicotinic receptors.
• This causes prolonged membrane depolarization and sustained K⁺ efflux through the receptor channel.
• Can cause dangerous hyperkalemia, especially in patients with burns, crush injuries, or denervation.

4. Cell Lysis

• Destruction of cells (e.g., in hemolysis, rhabdomyolysis, tumor lysis syndrome) releases the large intracellular K⁺ store directly into the bloodstream → hyperkalemia.

5. Serum Hyperosmolality → "Solute Drag"

• Hyperosmolality (e.g., severe hyperglycemia without insulin, mannitol) draws water out of cells by osmosis.
• As cell volume shrinks, intracellular K⁺ concentration rises, opening K⁺ channels.
• K⁺ follows water out of the cell — a mechanism called "solute drag" → hyperkalemia.

Key Clinical Takeaways

• Insulin + β-agonists are used in emergency hyperkalemia treatment precisely because they rapidly shift K⁺ into cells.
• Correcting DKA (acidosis) with insulin simultaneously drives K⁺ intracellularly — K⁺ supplementation is often needed.
• Digoxin toxicity is worsened by low K⁺, and its inhibition of the pump explains why it also elevates serum K⁺.