Sariban-Sohraby S, Mies F, Abramow M, Fisher R S
Laboratoire de Physiopathologie, Université Libre de Bruxelles, Belgium.
Am J Physiol. 1995 Mar;268(3 Pt 1):C557-62. doi: 10.1152/ajpcell.1995.268.3.C557.
Specific hydrolysis of GTP catalyzed by membranes prepared from A6 epithelial cells grown on porous supports was measured. Aldosterone treatment of the cells for 4 h increased Na+ transport and stimulated GTP hydrolysis by apical membranes in vitro more than twofold over basal levels. This stimulation was attributed to an increase in maximum velocity with little change in Michaelis-Menten constant values. Na+ transport rate and GTP hydrolysis were linearly correlated after aldosterone. This relationship was maintained when aldosterone's response was blunted by various inhibitors. Spironolactone decreased both the hormone-stimulated guanosinetriphosphatase (GTPase) and the Na+ transport rate. Pertussis toxin, which exerted minimal effects on basal rates, reduced the increase of Na+ current normally observed after aldosterone and the hormone stimulation of GTPase activity. The expression of classical Gi/Go-type G proteins was not increased after hormone treatment. When A6 cells were grown on nonporous plastic dishes, aldosterone neither stimulated GTPase activity nor increased amiloride-blockable 22Na+ fluxes. We propose that activation of one or more G proteins in the apical membrane of A6 cells is directly involved in the natriferic action of aldosterone.
对在多孔支持物上生长的A6上皮细胞制备的膜催化的GTP特异性水解进行了测定。用醛固酮处理细胞4小时可增加Na⁺转运，并使体外顶膜的GTP水解比基础水平提高两倍以上。这种刺激归因于最大速度的增加，而米氏常数的值变化不大。醛固酮处理后，Na⁺转运速率与GTP水解呈线性相关。当醛固酮的反应被各种抑制剂减弱时，这种关系仍然保持。螺内酯降低了激素刺激的鸟苷三磷酸酶（GTPase）和Na⁺转运速率。百日咳毒素对基础速率影响最小，它减少了醛固酮处理后通常观察到的Na⁺电流增加以及激素对GTPase活性的刺激。激素处理后，经典的Gi/Go型G蛋白的表达并未增加。当A6细胞在无孔塑料培养皿上生长时，醛固酮既不刺激GTPase活性，也不增加氨氯地平可阻断的²²Na⁺通量。我们提出，A6细胞顶膜中一种或多种G蛋白的激活直接参与醛固酮的促钠作用。
