Dehydroepiandrosterone sulfate-binding sites in plasma membrane from human uterine cervical fibroblasts. |
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Authors: | A Imai T Ohno T Tamaya |
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Institution: | Department of Obstetrics and Gynecology, Gifu University School of Medicine, Japan. |
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Abstract: | Dehydroepiandrosterone sulfate (DHA-S) plays a critical role in cervical dilatation at labor. Incubation of cervical fibroblasts with 3H]DHA-S caused a rapid and saturable increase in cellular radioactivity: an apparent equilibrium was reached by 2 min. There was no detectable conversion of DHA-S into DHA or oestradiol. When the fibroblasts loaded with 3H]DHA-S were homogenized and fractionated, the specific radioactivity in the plasma membrane fraction was enriched approximately 8- to 9-fold compared with the whole homogenate; only low amounts of radioactivity were observed in the other subcellular fractions. The binding of DHA-S to plasma membrane preparations showed saturation kinetics with an apparent equilibrium dissociation constant (Kd) of 12 nM, and the binding capacity (Bmax) was calculated to be 1.25 fmol/mg protein. Neither DHA nor oestrone sulfate affected 3H]DHA-S binding to the plasma membrane. The plasma membranes of skin fibroblasts did not show specific binding sites for DHA-S. These findings demonstrate the presence of specific binding sites for DHA-S in the plasma membrane of cervical stroma cells. The fetal adrenal steroid may exert its action on cervical ripening at least in part through membrane-associated binding sites, or receptors. |
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