Anand R J, Kanwar U, Sanyal S N
Department of Zoology, Panjab University, Chandigarh, India.
Indian J Exp Biol. 1996 Aug;34(8):786-93.
Brush border microvillous (BBM) and basal cell membranes (BCM) were isolated from syncytiotrophoblast of human term placenta by homogenization, sonication, prolonged stirring and differential centrifugation. Uptake of 45Ca(2+)-CaCl2 in membrane vesicles in morpholino propane sulphonic acid (MOPS) buffer was studied up to 60 min. Maximum uptake of the radioisotope was recorded at 10 and 15 min of incubation of the BBM and BCM, respectively. Radioisotopic uptake was also dependent on the Ca(2+)-concentration, linear up to 3 mu mole and then assuming hyperbolic substrate saturation kinetics. The Lineweaver-Burk transformation of the data gave Kt value for BBM and BCM, 0.85 and 1.08 microM, respectively while the Vmax of uptake (Jmax) in the same were 105.26 and 188.68 pmole Ca2+/microgram protein/20 min. Ca(2+)-Uptake in placental BBM and BCM vesicles was inhibited by two Ca(2+)-channel blockers, nifedipine and verapamil to as much as 50% while Ca(2+)-ionophore A23187 enhanced the uptake process significantly.
通过匀浆、超声处理、长时间搅拌和差速离心，从足月人胎盘的合体滋养层中分离出刷状缘微绒毛（BBM）和基底细胞膜（BCM）。在吗啉代丙烷磺酸（MOPS）缓冲液中，研究了膜囊泡中45Ca(2+)-CaCl2长达60分钟的摄取情况。分别在BBM和BCM孵育10分钟和15分钟时记录到放射性同位素的最大摄取量。放射性同位素的摄取也取决于Ca(2+)浓度，在3微摩尔之前呈线性，之后呈现双曲线底物饱和动力学。对数据进行Lineweaver-Burk转换后，BBM和BCM的Kt值分别为0.85和1.08微摩尔，而相同条件下摄取的Vmax（Jmax）分别为105.26和188.68皮摩尔Ca2+/微克蛋白质/20分钟。两种Ca(2+)通道阻滞剂硝苯地平和维拉帕米可抑制胎盘BBM和BCM囊泡中的Ca(2+)摄取多达50%，而Ca(2+)离子载体A23187则显著增强摄取过程。
