Evidence for carrier-mediated transport of glucocorticoids by human placental membrane vesicles.
Glucocorticoid uptake by isolated placental membrane vesicles has been studied in an attempt to identify a membrane-mediated carrier mechanism. A preliminary communication from this laboratory has reported that uptake of the glucocorticoid corticosterone by these vesicles was a time-dependent, saturable, osmotically sensitive process (Fant, M.E., Harbison, R.D. and Harrison, R.W. (1979) J. Biol. Chem. 254, 6218-6221), but did not conclusively demonstrate a carrier mechanism. Further studies of labeled corticosterone uptake by placental vesicles are described herein which indicate that steroid uptake by these vesicles is a carrier-mediated process. We found that corticosterone uptake was temperature-sensitive, and an apparent phase-transition effect on the rate of uptake was seen to occur at approximately 16 degrees C. Treatment of the vesicles with phospholipase A2 and the sulfhydryl group attacker, p-chloromercuriphenylsulfonate, inhibited corticosterone uptake. In contrast to our previous findings in intact cells, neuraminidase treatment of membranes did not inhibit steroid uptake, perhaps indicating a species variation. Lastly, it was possible to show that corticosterone movement across the membrane exhibited countertransport, a phenomenon common only to carrier-mediated transport mechanisms. These studies show that placental vesicles accumulate corticosterone by a carrier-mediated mechanism.
D000621:Aminoisobutyric Acids / Q000378:metabolism; D001693:Biological Transport, Active; D003345:Corticosterone / Q000378:metabolism; D005260:Female; D005938:Glucocorticoids / Q000378:metabolism*; D006801:Humans; D009439:Neuraminidase / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011402:Pronase / Q000378:metabolism
D000621:Aminoisobutyric Acids; D005938:Glucocorticoids; C100049:2-aminoisobutyric acid; D010741:Phospholipases A; D054467:Phospholipases A2; D009439:Neuraminidase; D011402:Pronase; D003345:Corticosterone