The Influence of Plasma Membrane Cholesterol on the Response of Adrenal Cells to Adrenocorticotropin*

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Abstract
The concentration of cholesterol in plasma membranes of Y-l cells was altered between values of the molar ratio of cholesterol to phospholipids (C/P) of 0.6:1.6 to study the influence of plasma membrane cholesterol on the response to ACTH. Increasing concentrations of membrane cholesterol (C/P) were associated with an increase in the number of ACTH receptors and, hence, production of cAMP and steroids without affecting the nature of binding (Kd) of ACTH to its receptor. Binding studies revealed spare ACTH receptors at all concentrations of membrane cholesterol. However, production of cAMP and steroids by Y-l cells were tightly coupled. Studies with cholera toxin snowed that extreme changes in C/P were without influence on the activity of Ns or that of the cyclase itself. It was also shown that production of steroids in the absence of ACTH and that in response to cholera toxin involve some effect of membrane cholesterol not dependent on cAMP. (Endocrinology120: 801–808, 1987)