It is well known that hypokalemia does not correct easily ifit is accompanied by hypomagnesemia. Amedical student I met looked into this topic and found a “Science in Renal Medicine”article. According to this article, one of the mechanisms throughwhich hypokalemia occurs in a hypomagnesemic state is through renal potassium wasting. Severalobservations have shown that magnesium infusion decreases renal K secretion inthe distal nephron.A study from Nature found that ROMK (akaKir), one of two potassium channels in the distal nephron, is responsible for thedistal renal K wasting in hypomagnesemia. The mechanism is that the intra-cellularfree Mg blocks the pore of the ROMK channel and limits potassium secretion in aconcentration-dependent manner; therefore low intracellular Mg level increasespotassium secretion.Some renal Mg wasting disorders (e.g. Mg channel TRPM6mutation) do not always present with hypokalemia. Why is that? The reason isthat you need 2 components for potassium excretion. One is increased Kpermeability of the ROMK, and the other is a driving force to secrete K like increaseddistal Na delivery or an elevated aldosterone level (via enhanced Na reabsorption in the distalnephron). It seems in these disorders you don’t have the second determinant forK secretion.Another fascinating renal physiology article! Now we arestill confused but have a better understanding of hypomagnesemia in a case ofhypokalemia. Posted by Tomoki Tsukahara
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