A patient receiving insulin and salbutamol infusion develops a fall in serum potassium within minutes. Which mechanism best explains this rapid transcellular shift of potassium?

• A Stimulation of the Na+-K+-ATPase pump in skeletal muscle ✓
• B Inhibition of the H+-K+-ATPase in the collecting duct
• C Increased aldosterone secretion acting on principal cells
• D Osmotic diuresis carrying potassium into the urine

Explanation

Insulin binds its receptor and activates tyrosine kinase signalling, while beta-2 agonists raise intracellular cAMP. Both increase Na+-K+-ATPase activity in skeletal muscle and liver, driving extracellular K+ into cells within minutes. Aldosterone acts on renal principal cells to promote urinary K+ excretion over hours to days, so it cannot explain a fall within minutes. Osmotic diuresis is also a renal route of loss, not a transcellular shift.

Reference: Ganong Review of Medical Physiology, 26th ed.

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