Miyai A, Yamauchi A, Nakanishi T, Sugita M, Takamitsu Y, Yokoyama K, Itoh T, Andou A, Kamada T, Ueda N
First Department of Medicine, Osaka University School of Medicine, Japan.
Kidney Int. 1995 Feb;47(2):473-80. doi: 10.1038/ki.1995.60.
Mesangial cells are considered to be faced with osmotic stress under physiological (such as extraglomerular mesangial cells) and pathophysiological (for example, diabetes mellitus) conditions. To see if mesangial cells have an osmoregulatory mechanism, like renal medullary cells, we measured the intracellular contents of organic osmolytes in isotonic and hypertonic conditions. Cultured rat mesangial cells are well tolerant of acute increase in osmolality up to 500 mOsm/kg. The myo-inositol content increased in hypertonic cells more than six-fold the value in isotonic cells. The contents of glycerophosphorylcholine and sorbitol also increased but were less than that of myo-inositol. The Na(+)-dependent myo-inositol uptake in hypertonic cells was a 12-fold uptake in isotonic cells, reaching a maximum 24 hours after the switch to a hypertonic medium. The uptake rate increased as medium osmolality increased from 300 to 500 mOsm/kg. Raffinose is the most effective solute to increase the myo-inositol uptake. NaCl, glucose and mannitol also increased the uptake rate (NaCl > glucose > mannitol). The increased uptake by hypertonicity was the result of an increase in Vmax without change in Km and was dependent on RNA and protein synthesis. These results indicate that mesangial cells respond to extracellular hypertonicity by increasing myo-inositol transport activity and accumulating myo-inositol into the cells, suggesting that myo-inositol functions as an organic osmolyte in mesangial cells.
在生理条件（如球外系膜细胞）和病理生理条件（如糖尿病）下，系膜细胞被认为面临渗透压应激。为了探究系膜细胞是否像肾髓质细胞一样具有渗透调节机制，我们在等渗和高渗条件下测量了有机渗透溶质的细胞内含量。培养的大鼠系膜细胞对高达500 mOsm/kg的渗透压急性升高具有良好的耐受性。高渗细胞中的肌醇含量增加，比等渗细胞中的值高出六倍多。甘油磷酸胆碱和山梨醇的含量也增加了，但低于肌醇。高渗细胞中依赖钠的肌醇摄取是等渗细胞中的12倍，在切换至高渗培养基后24小时达到最大值。摄取速率随着培养基渗透压从300 mOsm/kg增加到500 mOsm/kg而增加。棉子糖是增加肌醇摄取最有效的溶质。氯化钠、葡萄糖和甘露醇也增加了摄取速率（氯化钠>葡萄糖>甘露醇）。高渗导致的摄取增加是Vmax增加而Km不变的结果，并且依赖于RNA和蛋白质合成。这些结果表明，系膜细胞通过增加肌醇转运活性并将肌醇积累到细胞中来响应细胞外高渗，这表明肌醇在系膜细胞中作为一种有机渗透溶质发挥作用。
