Orsenigo M N, Tosco M, Esposito G, Faelli A
Dipartimento di Fisiologia e Biochimica Generali, Università di Milano, Italia.
Miner Electrolyte Metab. 1988;14(5):302-7.
Basolateral membranes isolated from rat jejunal enterocytes and enriched 14 times were found present as unsealed and sealed right side out (RSO) or inside out (IO) vesicles in the ratio 2:2:1. Entrance of 1 mM Na (JNa) into basolateral membrane vesicles was measured in the presence and in the absence of 5 mM ATP by a rapid filtration technique, under different experimental conditions. JNa across the basolateral membrane is cis-inhibited by K, transstimulated by K and further stimulated by ATP (activation of the Na pump). Both K- and ATP-positive effects are also obtained by other cations: the relative stimulation sequence is K greater than Rb = NH4 greater than Cs. The ATP effect can be suppressed by vanadate and strophanthidin; moreover the K effect on JNa is not influenced by blocking the mechanism of the Na pump with ouabain, strophanthidin and adenosine 5'-[beta,gamma-imido]triphosphate. The transmembrane potential does not influence the K-stimulated JNa. In addition to the Na pump this study demonstrates the existence of an exchange mechanism between Na and K, which seems to be different from the Na pump. There appears to be no Na-K cotransport.
从大鼠空肠肠上皮细胞分离并富集了14倍的基底外侧膜，发现其以未封闭和封闭的右侧向外（RSO）或向内向外（IO）囊泡的形式存在，比例为2:2:1。在不同实验条件下，通过快速过滤技术，在存在和不存在5 mM ATP的情况下，测量了1 mM Na（JNa）进入基底外侧膜囊泡的情况。跨基底外侧膜的JNa受到K的顺式抑制、K的反式刺激以及ATP的进一步刺激（钠泵激活）。其他阳离子也能产生K和ATP的阳性效应：相对刺激顺序为K＞Rb = NH4＞Cs。钒酸盐和毒毛花苷可抑制ATP效应；此外，用哇巴因、毒毛花苷和腺苷5'-[β,γ-亚氨基]三磷酸阻断钠泵机制不会影响K对JNa的作用。跨膜电位不影响K刺激的JNa。除了钠泵，本研究还证明了Na和K之间存在一种交换机制，这似乎与钠泵不同。似乎不存在Na-K共转运。
