Overview-potassium homeostasis

Renal: K excretion regulated at distal nephron (CCD) by principal & α-intercalated cells

• Distal Na delivery & urine flow: Na absorption → lumen electronegative → K secretion
• Metabolic alkalemia and aldosterone: increase Na absorption and K secretion
• nb, diurnal urinary K excretion (day >night), ∴ 24-h sample preferred over spot

Transcellular shifts

most common cause of acute ∆ in serum K (98% intracellular)

• Acid-base disturbance: K+/H+ exchange across cell membranes
• Insulin → stimulates Na-K ATPase → hypokalemia (mitigates postprandial ↑ K)
• Catecholamines → stimulate Na-K ATPase → hypokalemia; reversed by β-blockers
• Massive necrosis (eg, tumor lysis, rhabdo, ischemic bowel) → release of intracellular K
• Hypo- or hyperkalemic periodic paralysis: rare disorders due to channel mutations

Diet: alone rarely causes ↑ or ↓ K (total body store ~3500 mEq, daily intake ~100 mEq)

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