Cacciafesta M, Cammarella I, Ruggeri R, Germani M A, Soldo A R, Musca A
Istituto di I Clinica Medica, Università La Sapienza, Roma.
Recenti Prog Med. 1993 May;84(5):350-6.
Erythrocytes from a patient with hypokalemic periodic paralysis (HPP) have been studied, in order to investigate the presence of alterations of membrane cation active transport systems. An original 23Na-NMR method has been used, capable of evaluating quantitatively the Na+ efflux due to the Na+/K+/Cl- cotransport. This method uses a loading system to increase internal cellular Na+ concentration: in the patient with HPP both the internal Na+ concentration after loading and the Na+/K+/Cl- cotransport activity were decreased in comparison to the controls. Our data seem to confirm that the fall of K+ serum levels during attacks in HPP must be ascribed to a shift of K+ from extra- to intracellular compartment (with consequent changes in the fibrocellular membrane polarity), due to an alteration of membrane cation transport system: which does not only consist in a hyperactivity of Na+/K+ ATPase (already described by other AA.), but also in a "secondary" decreased K+ efflux driven by the cotransport. The decrease of cotransport activity may be considered as "compensatory" (in fact, the intracellular Na+ content is normal), since this transport system can work as a kind of "emergency" system that can "help" the ATPase-dependent pump in extruding any excess of cell Na+ content, or can be depressed by any decrease of this value, caused by an hyperactivity of the Na+/K+ ATPase. The decreased cotransport activity results in a powerful contribution to the increase of intracellular potassium due to the hyperactivity of the Na+/K+ pump. This method could supply a useful diagnostic marker in all uncertain cases.
为了研究膜阳离子主动转运系统是否存在改变，对一名低钾性周期性麻痹（HPP）患者的红细胞进行了研究。采用了一种新颖的23Na-NMR方法，该方法能够定量评估由Na+/K+/Cl-协同转运引起的Na+外流。此方法使用一种加载系统来提高细胞内Na+浓度：与对照组相比，HPP患者加载后的细胞内Na+浓度和Na+/K+/Cl-协同转运活性均降低。我们的数据似乎证实，HPP发作期间血清K+水平的下降必须归因于K+从细胞外转移到细胞内区室（从而导致纤维细胞膜极性改变），这是由于膜阳离子转运系统的改变所致：这不仅包括Na+/K+ ATP酶的活性过高（其他作者已描述过），还包括协同转运驱动的“继发性”K+外流减少。协同转运活性的降低可被视为“代偿性的”（事实上，细胞内Na+含量正常），因为该转运系统可作为一种“应急”系统，能够“协助”依赖ATP酶的泵排出任何过量的细胞内Na+含量，或者可能因Na+/K+ ATP酶活性过高导致该值降低而受到抑制。协同转运活性的降低对因Na+/K+泵活性过高导致的细胞内钾离子增加有很大贡献。在所有不确定的病例中，这种方法可以提供一个有用的诊断标志物。
