Knudsen T, Johansen T
Department of Pharmacology, Medical School, Odense University, Denmark.
Br J Pharmacol. 1989 Dec;98(4):1119-26. doi: 10.1111/j.1476-5381.1989.tb12655.x.
1 The inhibition by calcium of the Na(+)-K+ pump in the plasma membrane of rat peritoneal mast cells was studied in pure populations of the cells by measuring the ouabain-sensitive uptake of the radioactive potassium analogue, 86rubidium (86Rb+). 2 Exposure of the cells to calcium induced a time- and concentration-dependent decrease in the ouabain-sensitive K+(86Rb+)-uptake of the cells without influencing the ouabain-resistant uptake. The development of the inhibition required the presence of potassium in the medium in the millimolar range (1.5-8.0 mM), and it did not occur at a concentration of potassium (0.24 mM) that is probably rate limiting for the pump activity. In the presence of 1 mM calcium full inhibition developed almost immediately and was not readily reversed. The inhibition was not significantly reduced by 15 min incubation with 1.2 mM EGTA. 3 The inhibitory action of calcium did not develop when the mast cells were incubated in a potassium-free medium, which is known to block Na(+)-K+ pump activity and allow accumulation of sodium inside the cells. Likewise, increasing the sodium permeability of the plasma membrane by monensin abolished the inhibition of the pump activity. In both cases, incubation of the cells with 4.7 mM potassium and tracer amounts of 86Rb+ resulted in a very large uptake of K+ (86Rb+) into the cells (up to 2 nmol per 10(6) cells min-1), indicating a high activity of the Na(+)-K+ pump. 4. These observations support the view that long-term incubation of rat peritoneal mast cells in a calcium-free medium increases the permeability of the plasma membrane to sodium, and the consequent increase in the intracellular concentration of sodium causes an increase in the activity of the pump. Addition of calcium to the cell suspension decreases the sodium permeability, and hence the pump activity. This hypothesis is supported by the stimulation of pump activity produced by monensin, which is not inhibited by calcium. The enhancement of pump activity after exposure of calcium-deprived cells to EGTA might be the result of a further increase in the sodium permeability of the plasma membrane.
1 通过测量放射性钾类似物86铷（86Rb+）的哇巴因敏感摄取，在大鼠腹膜肥大细胞的纯细胞群体中研究了钙对质膜中Na(+)-K+泵的抑制作用。2 将细胞暴露于钙会导致细胞对哇巴因敏感的K+(86Rb+)摄取呈时间和浓度依赖性降低，而不影响对哇巴因不敏感的摄取。抑制作用的产生需要培养基中存在毫摩尔范围（1.5 - 8.0 mM）的钾，在可能是泵活性限速浓度的钾（0.24 mM）下不会发生抑制作用。在存在1 mM钙的情况下，几乎立即产生完全抑制且不易逆转。与1.2 mM乙二醇双四乙酸（EGTA）孵育15分钟并没有显著降低抑制作用。3 当肥大细胞在无钾培养基中孵育时，钙的抑制作用不会产生，已知无钾培养基会阻断Na(+)-K+泵活性并使细胞内钠积累。同样，莫能菌素增加质膜对钠的通透性会消除对泵活性的抑制。在这两种情况下，用4.7 mM钾和示踪量的86Rb+孵育细胞会导致细胞对K+(86Rb+)的摄取非常大（高达每10(6)个细胞每分钟2 nmol），表明Na(+)-K+泵活性很高。4. 这些观察结果支持以下观点：将大鼠腹膜肥大细胞在无钙培养基中长时间孵育会增加质膜对钠的通透性，细胞内钠浓度的随之增加会导致泵活性增加。向细胞悬液中添加钙会降低钠通透性，从而降低泵活性。莫能菌素产生的泵活性刺激支持了这一假设，莫能菌素不受钙抑制。钙缺乏细胞暴露于EGTA后泵活性的增强可能是质膜对钠通透性进一步增加的结果。
