Rattan V, Thind S K, Jethi R K, Nath R
Department of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh, India.
Magnes Res. 1993 Mar;6(1):3-10.
To examine the contribution of exogenous calcium and oxalate in magnesium deficiency, intestinal absorption of both calcium and oxalate was studied by preparing brush border membrane vesicles (BBMV). Purity of the BBMV was ascertained biochemically by enrichment of the marker enzyme alkaline phosphatase by 14-fold with a concomitant 90 per cent decrease in the basolateral marker enzyme Na+/K(+)-ATPase in the purified membrane preparation as compared to the respective homogenate in both the groups. Uptake studies were carried out by a rapid filtration technique. The kinetics were studied by measuring the rate of influx as a function of concentration (0.1-1.0 mM). BBMV from both the groups showed a linear positive relationship between the uptake rate and the concentration for both calcium and oxalate, thereby demonstrating that calcium and oxalate are transported through intestinal microvillus membrane by a simple passive diffusion process. However, the rate of uptake of calcium and oxalate was significantly higher in the magnesium-deficient group as compared to the pair-fed control group, as shown by the increase in the slope line for both calcium and oxalate (for calcium, control = 3.88, deficient = 5.86; for oxalate, control = 4.41, deficient = 7.20). Analysis of the lipid composition of the BBM revealed a significant decrease in the cholesterol content (P < 0.01) with a concomitant increase in the triglycerides (P < 0.01) and total fatty acid content (P < 0.001) in the magnesium-deficient group. Thus the results indicate that, although the mechanism of translocation of calcium and oxalate in the intestine is similar in the two groups, magnesium deficiency leads to hyperabsorption of both the ligands through alterations in the lipid composition of the membrane, thereby increasing the risk of stone formation.
为研究外源性钙和草酸盐在镁缺乏中的作用，通过制备刷状缘膜囊泡（BBMV）来研究钙和草酸盐的肠道吸收。通过将标记酶碱性磷酸酶富集14倍，同时与两组各自的匀浆相比，纯化膜制剂中的基底外侧标记酶Na+/K(+)-ATP酶降低90%，从生化角度确定了BBMV的纯度。采用快速过滤技术进行摄取研究。通过测量流入速率作为浓度（0.1-1.0 mM）的函数来研究动力学。两组的BBMV均显示钙和草酸盐的摄取速率与浓度之间呈线性正相关，从而表明钙和草酸盐通过简单的被动扩散过程穿过肠道微绒毛膜。然而，与配对喂养的对照组相比，镁缺乏组中钙和草酸盐的摄取速率显著更高，这通过钙和草酸盐的斜率线增加得以体现（钙，对照组=3.88，缺乏组=5.86；草酸盐，对照组=4.41，缺乏组=7.20）。对BBM脂质组成的分析显示，镁缺乏组中胆固醇含量显著降低（P<0.01），同时甘油三酯（P<0.01）和总脂肪酸含量增加（P<0.001）。因此，结果表明，尽管两组中钙和草酸盐在肠道中的转运机制相似，但镁缺乏通过改变膜的脂质组成导致两种配体的过度吸收，从而增加结石形成的风险。
