Hanson G L, Schilling W P, Michael L H
Department of Medicine, Baylor College of Medicine, Houston, Texas 77030.
Am J Physiol. 1993 Feb;264(2 Pt 2):H320-6. doi: 10.1152/ajpheart.1993.264.2.H320.
The purpose of this study was to determine whether the Na(+)-K+ pump and the Na(+)-Ca2+ exchanger, two systems thought to be important in excitation-contraction coupling in the heart, change during postnatal development. In adult and neonatal canine cardiac sarcolemmal preparations, Na(+)-K(+)-adenosine-triphosphatase (ATPase) activity and specific [3H]ouabain binding were found to be higher in the adult compared with the neonate, although Na(+)-K(+)-ATPase turnover numbers were not significantly different. Furthermore, ouabain association and dissociation rate constants, examined under a variety of conditions, were the same for both the neonate and adult preparations. These results suggest that the number of pump units per milligram sarcolemmal protein changes during postnatal development. In contrast, the initial rate of Na(+)-dependent-45Ca2+ influx, an index of Na(+)-Ca2+ exchange activity, was not significantly different in the two age groups. Additionally, the sensitivity of the exchanger to extravesicular Ca2+ and K+ was the same. In summary, during postnatal development sarcolemmal Na(+)-K(+)-ATPase and [3H]ouabain binding increase from neonate to adult, whereas Na(+)-Ca2+ exchange activity remains the same. This may result in a greater importance of Ca2+ flux through the Na(+)-Ca2+ exchange system in the neonate compared with the adult.
本研究的目的是确定钠钾泵和钠钙交换体这两个在心脏兴奋-收缩偶联中被认为很重要的系统在出生后发育过程中是否发生变化。在成年和新生犬心脏肌膜制剂中，发现成年犬的钠钾-腺苷三磷酸酶（ATP酶）活性和特异性[3H]哇巴因结合比新生犬更高，尽管钠钾-ATP酶的转换数没有显著差异。此外，在各种条件下检测的哇巴因结合和解离速率常数在新生和成年制剂中是相同的。这些结果表明，每毫克肌膜蛋白的泵单位数量在出生后发育过程中发生变化。相比之下，钠依赖性45Ca2+内流的初始速率（钠钙交换活性的指标）在两个年龄组中没有显著差异。此外，交换体对细胞外Ca2+和K+的敏感性是相同的。总之，在出生后发育过程中，肌膜钠钾-ATP酶和[3H]哇巴因结合从新生犬到成年犬增加，而钠钙交换活性保持不变。这可能导致与成年犬相比，新生犬中通过钠钙交换系统的Ca2+通量更为重要。
