Ricote M, Garcia-Martin E, Sancho J, Gutierrez-Merino C
Departamento de Bioquímica y Biología Molecular y Genética, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain.
Hypertension. 1997 Jun;29(6):1337-43. doi: 10.1161/01.hyp.29.6.1337.
We have isolated from bovine hypothalamic and pituitary tissues a sodium pump inhibitor that is structurally different from ouabain. By mass spectrometric analysis, this purified factor revealed a single unique molecular ion with an accurate mass of 412.277 and a mass spectra different from that of ouabain. It has been previously shown that this factor inhibits the Ca2+, Mg(2+)-ATPase of the plasma membrane of synaptosomes. Because Ca2+ plays a major role in cellular excitability, we carried out a systematic study of the effects of this inhibitor on the Ca2+ transport processes across the plasma membrane of synaptosomes: We measured ATP-dependent calcium uptake, Na(+)-Ca2+ exchange, and passive permeability using 45Ca2+ and Millipore filtration, chlortetracycline fluorescence, and light-scattering, respectively. This factor inhibits the Na+, K(+)-ATPase activity of the synaptosomal plasma membrane vesicles in the same range of concentrations that produced an increase of intrasynaptosomal free calcium, with nearly the same K0.5 value. In addition, in this concentration range, this factor stimulated 10- to 11-fold the passive flux of Ca2+ and 2.5- to 3-fold the Ca2+ influx via the Na(+)-Ca2+ exchange in these membranes with respect to control values. Measurements of fluorescence anisotropy showed that in this concentration range, the inhibitor did not significantly change the order parameter (fluidity) of these membranes. These results suggest that besides its known inhibition of the sodium pump, this factor could play a role in the control of Ca2+ homeostasis by direct modulation of transport systems implicated in the control of intracellular calcium.
我们已从牛下丘脑和垂体组织中分离出一种钠泵抑制剂，其结构与哇巴因不同。通过质谱分析，这种纯化因子显示出一个单一的独特分子离子，精确质量为412.277，质谱与哇巴因不同。先前已表明，该因子可抑制突触体细胞膜的Ca2 +、Mg(2 +)-ATP酶。由于Ca2 +在细胞兴奋性中起主要作用，我们对该抑制剂对突触体细胞膜Ca2 +转运过程的影响进行了系统研究：我们分别使用45Ca2 +和微孔过滤、金霉素荧光和光散射测量了ATP依赖性钙摄取、Na(+)-Ca2 +交换和被动通透性。该因子在产生突触体内游离钙增加的相同浓度范围内抑制突触体细胞膜囊泡的Na +、K(+)-ATP酶活性，K0.5值几乎相同。此外，在此浓度范围内，相对于对照值，该因子刺激这些膜中Ca2 +的被动通量增加10至11倍，通过Na(+)-Ca2 +交换的Ca2 +流入增加2.5至3倍。荧光各向异性测量表明，在此浓度范围内，抑制剂并未显著改变这些膜的有序参数（流动性）。这些结果表明，除了已知的对钠泵的抑制作用外，该因子可能通过直接调节参与细胞内钙控制的转运系统，在Ca2 +稳态控制中发挥作用。
