Enyedi A, Brandt J, Minami J, Penniston J T
Department of Biochemistry and Molecular Biology, Mayo Clinic/Foundation, Rochester, MN 55905.
Biochem J. 1989 Jul 1;261(1):23-8. doi: 10.1042/bj2610023.
Development of myometrium in young female rats was stimulated by administration of diethylstilboestrol. Plasma membrane and sarcoplasmic reticulum from rat myometrium were separated by a new and rapid method using a Percoll gradient. Calcium uptake was inhibited in plasma membrane vesicles isolated from oxytocin-treated myometrium, while no consistent effect of oxytocin was found on the Ca2+ uptake in the sarcoplasmic reticulum. Oxytocin regulated the plasma membrane Ca2+ pump by decreasing its apparent affinity for Ca2+ without affecting its maximal velocity. The K1/2 for Ca2+ in the absence of calmodulin was 0.41 +/- 0.04 microM in normal membranes; this was increased to 0.93 +/- 0.12 microM in oxytocin-treated membranes. Calmodulin decreased the K1/2 for Ca2+ to 0.27 +/- 0.027 microM and oxytocin also increased this, to 0.46 +/- 0.061 microM. The effect of oxytocin on the plasma membrane Ca2+ pump was highly dependent on the hormonal status of the animals. When the diethylstilboestrol was administered together with progesterone, the inhibitory action of oxytocin was totally suppressed, consistent with the expected action of this agent. The results suggest that regulation of the plasma membrane Ca2+ pump may be important in the prolonged elevation of intracellular Ca2+ caused by oxytocin.
己烯雌酚的给药刺激了年轻雌性大鼠子宫肌层的发育。采用一种新的快速方法，利用Percoll梯度分离大鼠子宫肌层的质膜和肌浆网。从经催产素处理的子宫肌层分离的质膜囊泡中的钙摄取受到抑制，而未发现催产素对肌浆网中的Ca2+摄取有一致的影响。催产素通过降低其对Ca2+的表观亲和力而不影响其最大速度来调节质膜Ca2+泵。在无钙调蛋白的情况下，正常膜中Ca2+的K1/2为0.41±0.04 microM；在经催产素处理的膜中，该值增加到0.93±0.12 microM。钙调蛋白将Ca2+的K1/2降低到0.27±0.027 microM，而催产素也将其增加到0.46±0.061 microM。催产素对质膜Ca2+泵的作用高度依赖于动物的激素状态。当将己烯雌酚与孕酮一起给药时，催产素的抑制作用被完全抑制，这与该药物的预期作用一致。结果表明，质膜Ca2+泵的调节可能在催产素引起的细胞内Ca2+的长期升高过程中起重要作用。
