SARCOLEMMAL NA+-CA-2+ EXCHANGE ACTIVITY AND EXCHANGER IMMUNOREACTIVITY IN DEVELOPING RABBIT HEARTS
SARCOLEMMAL NA+-CA-2+ EXCHANGE ACTIVITY AND EXCHANGER IMMUNOREACTIVITY IN DEVELOPING RABBIT HEARTS
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DOI：
10.1152/ajpheart.1992.263.5.h1506
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发表时间：
1992-11-01
影响因子：
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通讯作者：
ARTMAN, M
中科院分区：
文献类型：
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作者：
ARTMAN, M
有人推测，由于肌浆网不发达，肌膜Na+-Ca~(2+)交换在调节发育中的心肌细胞内的Ca~(2+)流量方面具有相对更重要的作用。为了探索这一概念，我们从胎儿晚期(妊娠28天)、新生儿(24-48小时)、未成熟(14-16天)和成年新西兰大白兔制备了心肌肌膜囊泡。通过将含钠囊泡(140 MM)稀释到无钠缓冲液中，并通过定时猝灭和快速过滤测量钙摄取(40微米钙)来测量钠依赖的钙摄取。四个年龄组的囊泡均表现出Na+-Ca~(2+)交换的钙摄取曲线，该曲线可被呋喃霉素刺激，而被阿米洛利抑制。胎儿(23.2+/-5.5nmol/mg)和新生儿(26.2+/-5.9nmol/mg)的初始摄取速度(在2 S时测量并校正了活性囊泡的分数)显著高于成人肌膜标本(7.3nmol/-1.2nmol/mg)。2周龄组摄取居中(13.7+/-1.7nmol/mg)。用抗Na+-Ca~(2+)交换蛋白的多克隆抗体测定免疫反应性，比较交换蛋白的相对含量。蛋白质槽印迹密度扫描显示，胎儿和新生儿肌膜中的交换蛋白大约是成人标本的2.5倍。检测到的交换蛋白的相对数量与观察到的与年龄相关的交换活性差异在免疫学上是一致的。因此，心肌细胞膜Na~+-Ca~(2+)交换器在胎晚期/新生早期兔心脏中含量丰富，功能发达，出生后呈下降趋势。这些结果支持了Na~+-Ca~(2+)交换在围产期心肌细胞Ca~(2+)调节中起主导作用的假说。
It has been postulated that as a consequence of an underdeveloped sarcoplasmic reticulum, sarcolemmal Na+-Ca2+ exchange assumes relatively greater importance in modulating Ca2+ fluxes in the developing heart. To explore this concept, cardiac sarcolemmal vesicles were prepared from late fetal (28-day gestation), newborn (24-48 h), immature (14-16 days), and adult New Zealand White rabbits. Na+-dependent Ca2+ uptake was measured by diluting Na+-loaded (140 mM) vesicles into Na+-free buffer and measuring Ca-45(2+) uptake (40 muM Ca2+) by timed quenching and rapid filtration. Vesicles from all four age groups demonstrated Ca2+ uptake curves characteristic of Na+-Ca2+ exchange with stimulation by valinomycin and inhibition by amiloride. Initial uptake velocity (measured at 2 s and corrected for the fraction of competent vesicles) was significantly higher in fetal (23.2 +/- 5.5 nmol/mg) and newborn (26.2 +/- 5.9 nmol/mg) than in adult sarcolemmal preparations (7.3 +/- 1.2 nmol/mg). Uptake was intermediate in the 2-wk-old group (13.7 +/- 1.7 nmol/mg). The relative amounts of exchanger protein were compared by quantitating immunoreactivity using a polyclonal antibody to the Na+-Ca2+ exchanger. Densitometric scanning of protein slot blots demonstrated approximately 2.5 times more exchanger protein in fetal and newborn sarcolemma than in adult preparations. The relative amount of exchanger protein detected immunologically corresponded with the age-related differences observed in exchanger activity. Thus the cardiac sarcolemmal Na+-Ca2+ exchanger is abundant and functionally well-developed in the late fetal/early newborn rabbit heart and appears to decline postnatally. These results support the hypothesis that Na+-Ca2+ exchange plays a predominant role in the regulation of cardiac myocellular Ca2+ during perinatal maturation.