Localization of the Oxytocin Receptor in the Plasma Membrane of Rat Myometrium

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Abstract
The distribution of [3H]oxytocin binding sites among various subcellular fractions of rat myometrium paralleled the distribution of 5''-nucleotidase, a plasma membrane marker enzyme, but not of NADPH-cytochrome c reductase or succinate-cytochrome c reductase, which are endoplasmic reticulum and mitochondrial marker enzymes, respectively. [3H]Oxytocin binding to the most enriched plasma membrane fraction showed the degree of selectivity with respect to hormone analogues that is expected for the oxytocin receptor. The binding of oxytocin to this fraction showed an apparent Kd of 1.98 .times. 10-9 M and a capacity of 1.28 pmol mg-1. The oxytocin receptor is probably located on the plasma membrane of the smooth muscle cells of the rat uterus.