Quamme G A, Dirks J H
Am J Physiol. 1980 Mar;238(3):F187-98. doi: 10.1152/ajprenal.1980.238.3.F187.
Magnesium and calcium transport was studied in the superficial proximal tubule, loop of Henle, and superficial distal tubule of the rat by in vivo microperfusion. Magnesium chloride was used to vary plasma and perfusate magnesium concentration. Perfusion with magnesium-free Ringer solution resulted in little magnesium entry into the tubule lumen in either normomagnesemic or hypermagnesemic rats. Magnesium concentration increased with water abstraction along the perfused proximal tubule whether markedly above or below plasma concentrations. Absolute proximal magnesium reabsorption increased with perfusate concentration; however, fractional magnesium and calcium reabsorption decreased in proportion to net sodium reabsorption with elevated extracellular magnesium. Magnesium absorption increased in the loop of Henle proportional to luminal magnesium concentration. Sodium and calcium reabsorption was not affected. Acute elevation of plasma magnesium, however, significantly depressed absolute magnesium reabsorption to a greater degree than calcium whereas sodium was unchanged. The effects of extracellular magnesium onloop reabsorption were reflected in the final urine. Reabsorption of sodium, calcium, and magnesium in the perfused distal tubule was concentration-dependent and not altered by luminal or extracellular magnesium concentration.
通过体内微灌注研究了大鼠浅表近端小管、髓袢和浅表远端小管中的镁和钙转运。使用氯化镁来改变血浆和灌注液中的镁浓度。用无镁林格溶液灌注时，无论是正常镁血症还是高镁血症大鼠，进入小管腔的镁都很少。无论明显高于还是低于血浆浓度，沿着灌注的近端小管，镁浓度都随着水分的重吸收而增加。绝对近端镁重吸收随着灌注液浓度的增加而增加；然而，随着细胞外镁升高，镁和钙的分数重吸收与净钠重吸收成比例下降。髓袢中的镁吸收与管腔镁浓度成比例增加。钠和钙的重吸收不受影响。然而，血浆镁的急性升高比钙更显著地降低了绝对镁重吸收，而钠则没有变化。细胞外镁对髓袢重吸收的影响反映在最终尿液中。灌注远端小管中钠、钙和镁的重吸收是浓度依赖性的，不受管腔或细胞外镁浓度的影响。
