CARDIOTONIC STEROIDS FROM THE ADRENAL GLAND

钠钾ATPase(NKA，即钠泵)活性的调节是维持细胞外液容量和血压的关键因素。当酶停留在细胞膜的功能位置时，在细胞内和细胞外表面都有可能对酶进行调节。在细胞内表面，该酶受细胞表面体液物质受体的信号调节，如血管紧张素II、多巴胺和去甲肾上腺素。现在有证据表明，这些信号通过改变NKA的亚细胞分布(内体隔离)来改变NKA产生的载体运输。在其细胞外表面，NKA投射出一个高度保守的强心类固醇结合部位，它是酶的组成部分，除了以高亲和力结合强心类固醇外，没有其他功能。我们实验室最近的工作和该领域其他人的工作已经确定了通过强心类固醇受体与酶结合并抑制酶的物质的化学特性。我们已经证明这种抑制物是由肾上腺皮质合成的内源性物质。本研究将进一步加深我们对肾上腺皮质强心激素功能的认识。本研究将进一步加深我们对肾上腺皮质强心激素功能的认识。我们将描述导致内源性肾上腺强心类固醇形成的生物合成途径的重要特征。我们将研究胆固醇和胆固醇侧链断裂在导致肾上腺强心类固醇产生的代谢途径中的作用。我们将研究这种新的类固醇激素表面受体的活性控制。最后，我们将检查和表征肾上腺强心类固醇与其在肾钠钾ATPase上的受体结合部位之间的相互作用。我们还将确定与该位点的相互作用是否与体液物质对ATPase活性的调节相协调，以及这种协调机制是否通过增加对受体蛋白的隔离而发生。

Regulation of the activity of sodium, potassium-ATPase (NKA, the sodium pump) is a critical element in the maintenance of extracellular fluid volume and blood pressure. When the enzyme is resident in its functional location in the cell membrane, regulation of the enzyme is possible at both the intracellular and extracellular surfaces. At the intracellular surface the enzyme is regulated by signals arising from cell surface receptors for humoral substances such as angiotensin II, dopamine and norepinephrine. There is now evidence that these signals alter the vectorial transport produced by NKA by changing its subcellular distribution (endosomal sequestration). At its extracellular surface, NKA projects a highly conserved cardiotonic steroid binding site which is an integral part of the enzyme and which serves no other function except to bind cardiotonic steroids with high affinity. Recent work in our laboratory and work by others in the field has defined the chemical identity of substances which bind to and inhibit the enzyme through the cardiotonic steroid receptor. We have shown that this inhibitor is an endogenous substance synthesized by the adrenal cortex. The present studies will further refine our understanding of the function of adrenocortical cardiotonic steroid. The present studies will further refine our understanding of the function of adrenocortical cardiotonic steroid. We will delineate important features of the biosynthetic pathway which leads to formation of the endogenous adrenal cardiotonic steroid. We will examine the role of cholesterol and cholesterol side chain cleavage in the metabolic pathway leading to the production of adrenal cardiotonic steroid. We will examine the control of activity in this novel steroidogenic surface receptors. Finally, we will examine and characterize the interaction between adrenal cardiotonic steroid and its receptor binding site on renal sodium, potassium-ATPase. We will also determine if the interaction with this site coordinates with regulation of ATPase activity by humoral substances and whether the mechanism of coordination occurs through increased sequestration of the receptor protein.