A patient has low serum magnesium but normal calcium and presents with palpitations and elevated blood pressure. Which mechanism best explains how magnesium deficiency could contribute to these findings?

• A. Magnesium deficiency selectively stimulates aldosterone receptors in the arterial wall independent of the renin–angiotensin system, instantly doubling blood pressure without affecting cardiac rhythm.
• B. Magnesium deficiency impairs vascular smooth muscle relaxation and cardiac ion channel regulation, increasing vascular tone and arrhythmia risk, which can raise blood pressure and cause palpitations.
• C. Hypomagnesemia blocks renal sodium reabsorption so effectively that extracellular volume always falls, and this fall in volume is the direct cause of the observed elevated blood pressure and arrhythmias.
• D. Low magnesium directly increases parathyroid hormone secretion causing acute hypercalcemia that then immediately causes palpitations and hypertension in all patients.

Answer: (B)