Ruete María Celeste, Carrizo Liliana C, Bocanegra María Victoria, Vallés Patricia G
IMBECU-CONICET (Consejo Nacional de Investigaciones Científicas y Tecnológicas), Mendoza, Argentina.
Nephron Physiol. 2009;111(3):p17-29. doi: 10.1159/000199462. Epub 2009 Feb 6.
Potassium depletion has been associated with altered sodium reabsorption in tubule segments. We studied if the altered abundance of Na(+) transporters and ROMK are associated with distal potassium secretion that contributes to the development of hypokalemia in protein-deprived rats. After weaning, Wistar rats were fed with a low-protein diet (8%, LP) for 14 days and then recovered with a normal-protein (NP) diet (24%, RP). An age-matched control group was fed with an NP diet (24%, NP). We showed hypokalemia, lower glomerular filtration rate and higher FEK(+) in the LP group. Immunoblotting revealed that the type 3 Na(+)/H(+) exchanger in the cortex was decreased in the LP group. However, the type 2 Na(+)-K(+)-2Cl(-) cotransporter was increased in the outer stripe of the outer medulla in the LP group. The abundance of the aldosterone-regulated Na(+)-Cl(-) cotransporter (NCC) and epithelial Na(+) channel (ENaC) was higher in the LP group and was associated with higher plasma aldosterone level. ROMK protein levels were increased. Na(+)/K(+)-ATPase protein levels were the same in both groups. After the recovery period, the expression of Na(+) transporters and ROMK returned to control values. We conclude that increased expression of NCC, ENaC subunits, and ROMK contributed to distal potassium secretion leading to enhanced potassium excretion, which may explain the hypokalemia resulting from LP feeding. A role of aldosterone may be suggested.
钾缺乏与肾小管节段钠重吸收改变有关。我们研究了Na(+)转运体和ROMK丰度的改变是否与远端钾分泌有关，而远端钾分泌会导致蛋白质缺乏大鼠低钾血症的发生。断奶后，将Wistar大鼠用低蛋白饮食（8%，LP）喂养14天，然后用正常蛋白（NP）饮食（24%，RP）恢复。一个年龄匹配的对照组用NP饮食（24%，NP）喂养。我们发现LP组存在低钾血症、较低的肾小球滤过率和较高的FEK(+)。免疫印迹显示，LP组皮质中的3型Na(+)/H(+)交换体减少。然而，LP组外髓质外层条纹中的2型Na(+)-K(+)-2Cl(-)共转运体增加。LP组中醛固酮调节的Na(+)-Cl(-)共转运体（NCC）和上皮Na(+)通道（ENaC）的丰度较高，且与较高的血浆醛固酮水平相关。ROMK蛋白水平增加。两组的Na(+)/K(+)-ATP酶蛋白水平相同。恢复期后，Na(+)转运体和ROMK的表达恢复到对照值。我们得出结论，NCC、ENaC亚基和ROMK表达的增加导致远端钾分泌，从而增强钾排泄，这可能解释了LP喂养导致的低钾血症。这提示了醛固酮的作用。
