Armbrecht H J, Boltz M A, Wongsurawat N
Geriatric Research, Education and Clinical Center, Department of Veterans Affairs Medical Center, St. Louis, MO 63125.
Biochim Biophys Acta. 1994 Oct 12;1195(1):110-4. doi: 10.1016/0005-2736(94)90016-7.
The capacity of the small intestine to actively transport Ca declines markedly with increasing age in the rat. The basal-lateral plasma membrane Ca pump is thought to be an important component of the active transport mechanism. Therefore, the purpose of this study was to determine if there are changes in the expression of the intestinal Ca pump with age, mRNA levels were quantitated by Northern and dot blot analysis using a cDNA probe based on the sequence of the plasma membrane Ca pump expressed in the rat intestine (PMCA1). In the duodenum, Ca pump mRNA levels were 3-4 times higher in young (2 months) rats compared to adult (12 months) and old (27 months) rats. In the ileum, Ca pump mRNA levels were one third those of the duodenum, and ileal levels were higher in young rats compared to adult rats. These changes in mRNA levels with age and segment were significantly correlated with Ca pump activity as measured in basal-lateral membrane vesicles in vitro. To determine intestinal responsiveness to 1,25(OH)2D, rats were fed a strontium diet to induce vitamin D deficiency. In young animals, 1,25(OH)2D significantly increased Ca pump mRNA levels 4-fold in the duodenum. 1,25(OH)2D had a similar effect in the adult duodenum. These studies demonstrate that there are changes in Ca pump mRNA levels with age and intestinal segment. Since there was no change in the capacity of 1,25(OH)2D to increase Ca pump mRNA levels, the decline in Ca pump expression may be due to the age-related decrease in serum 1,25(OH)2D rather than to decrease responsiveness to 1,25(OH)2D.
在大鼠中，小肠主动转运钙的能力会随着年龄的增长而显著下降。基底外侧质膜钙泵被认为是主动转运机制的一个重要组成部分。因此，本研究的目的是确定肠道钙泵的表达是否随年龄变化，使用基于大鼠肠道中表达的质膜钙泵（PMCA1）序列的cDNA探针，通过Northern印迹和斑点印迹分析对mRNA水平进行定量。在十二指肠中，与成年（12个月）和老年（27个月）大鼠相比，幼年（2个月）大鼠的钙泵mRNA水平高3至4倍。在回肠中，钙泵mRNA水平是十二指肠的三分之一，并且幼年大鼠的回肠水平高于成年大鼠。这些mRNA水平随年龄和肠段的变化与体外基底外侧膜囊泡中测得的钙泵活性显著相关。为了确定肠道对1,25(OH)2D的反应性，给大鼠喂食锶饮食以诱导维生素D缺乏。在幼年动物中，1,25(OH)2D使十二指肠中的钙泵mRNA水平显著增加4倍。1,25(OH)2D在成年十二指肠中也有类似作用。这些研究表明，钙泵mRNA水平随年龄和肠段而变化。由于1,25(OH)2D增加钙泵mRNA水平的能力没有变化，钙泵表达的下降可能是由于与年龄相关的血清1,25(OH)2D减少，而不是对1,25(OH)2D的反应性降低。
