Shibata H, Ghishan F K
Department of Pediatric Gastroenterology, Vanderbilt University, Nashville, Tennessee 37232.
Proc Soc Exp Biol Med. 1990 May;194(1):26-31. doi: 10.3181/00379727-194-43049.
Calcium transport across the basolateral membranes of the enterocyte represents the active step in calcium translocation. This step occurs by two mechanisms, an ATP-dependent pump and a Ca2+/Na+ exchange process. These studies were designed to investigate these two processes in jejunal basolateral membrane vesicles (BLMV) of the spontaneously hypertensive rats (SHR) and their genetically matched controls, Wistar-Kyoto (WKY) rats. The ATP-dependent calcium uptake was stimulated several-fold compared with no ATP condition in both SHR and WKY, but no differences were noted between rate of calcium uptake in SHR and WKY. Kinetics of ATP-dependent calcium uptake at concentrations between 0.01 and 1.0 microM revealed a Vmax of 0.67 +/- 0.03 nmol/mg protein/20 sec and a Km of 0.2 +/- 0.03 microM in SHR and Vmax of 0.69 +/- 0.12 and a Km of 0.32 +/- 0.14 microM in WKY rats. Ca2+/Na+ exchange in jejunal BLMV of SHR and WKY was investigated in two ways. First, sodium was added to the incubation medium (cis-Na+). Second, Ca2+ efflux from BLMV was studied in the presence of extravesicular Na+ (trans-Na+). Both studies suggest a decreased exchange of calcium and Na+. Kinetic parameters of Na(+)-dependent Ca2+ uptake at concentrations between 0.01 and 1.0 microM exhibited Vmax of 0.05 +/- 0.01 nanmol/mg protein/5 sec and a Km of 0.21 +/- 0.13 microM in SHR and Vmax of 0.11 +/- 0.02 nanmol/mg protein/5 sec and a Km of 0.09 +/- 0.05 in WKY, respectively. These results confirm that the intestinal BLMV of SHR and WKY rats have two mechanisms for calcium extrusion, an ATP-dependent Ca2+ transport process and a Na+/Ca2+ exchange process. The ATP-dependent process appears to be functional in SHR; however, the Ca2+/Na+ exchange mechanism appears to have a marked decrease in its maximal capacity. These findings suggest that calcium extrusion via Ca2+/Na+ is impaired in the SHR, which may lead to an increase in intracellular calcium concentration. These findings may have relevance to the development of hypertension.
钙穿过肠上皮细胞基底外侧膜的转运是钙转运过程中的主动步骤。这一步骤通过两种机制发生，一种是ATP依赖泵，另一种是Ca2+/Na+交换过程。这些研究旨在探讨自发性高血压大鼠（SHR）及其基因匹配的对照Wistar-Kyoto（WKY）大鼠空肠基底外侧膜囊泡（BLMV）中的这两个过程。与无ATP条件相比，SHR和WKY中ATP依赖的钙摄取均增加了几倍，但SHR和WKY的钙摄取速率之间未发现差异。在0.01至1.0 microM浓度下ATP依赖的钙摄取动力学显示，SHR的Vmax为0.67±0.03 nmol/mg蛋白质/20秒，Km为0.2±0.03 microM；WKY大鼠的Vmax为0.69±0.12，Km为0.32±0.14 microM。通过两种方式研究了SHR和WKY空肠BLMV中的Ca2+/Na+交换。首先，将钠添加到孵育培养基中（顺式Na+）。其次，在囊泡外存在Na+（反式Na+）的情况下研究了BLMV中的Ca2+流出。两项研究均表明钙和钠的交换减少。在0.01至1.0 microM浓度下Na+依赖的Ca2+摄取动力学参数显示SHR的Vmax为0.05±0.0l nmol/mg蛋白质/5秒，Km为0.21±0.13 microM；WKY的Vmax为0.11±0.02 nmol/mg蛋白质/5秒，Km为0.09±0.05。这些结果证实，SHR和WKY大鼠的肠BLMV有两种钙排出机制，一种是ATP依赖的Ca2+转运过程，另一种是Na+/Ca2+交换过程。ATP依赖过程在SHR中似乎起作用；然而，Ca2+/Na+交换机制的最大能力似乎有显著下降。这些发现表明，SHR中通过Ca2+/Na+的钙排出受损，这可能导致细胞内钙浓度升高。这些发现可能与高血压的发生有关。
