The mechanism of [3H]dexamethasone uptake into prolactin producing rat pituitary cells (GH3 cells) in culture.
Glucocorticosteroids stimulate growth hormone (GH) synthesis and inhibit prolactin (PRL) synthesis and cell growth in cultured GH3 cells, a clonal cell strain derived from a rat pituitary tumour. This model system was used to study the mechanism by which glucocorticosteroids enter target cells. The cellular uptake of [3H]dexamethasone was temperature dependent and was further inhibited by addition of an excess amount of cold dexamethasone. Half maximal uptake was obtained after about 5 min at 37 degrees C. The initial rates of [3H]dexamethasone uptake were a linear function of the extracellular hormone concentration. The uptake of [3H]dexamethasone in intact cells studied at different temperatures resulted in linear Arrhenius plots, with a calculated energy of activation of 91.0 kJ x mole-1 x degree-1. Scatchard analysis of specifically cell bound [3H]dexamethasone at equilibrium (0 degrees C) showed a straight line with a calculated dissociation constant (Kd) of 1.6 x 10(-9) M and a maximal uptake of 180 x 10(-15) mole/mg cell protein. Specific binding of [3H]dexamethasone to cytosol proteins could only be demonstrated at 0 degrees C. These results indicate that [3H]dexamethasone diffuses passively into the cell, and binds to specific receptors in an energy dependent way.
Furu
K
K
Institute of Physiology, University of Oslo, Norway.
Kilvik
K
K
Gautvik
K M
KM
Haug
E
E
D000818:Animals; D003907:Dexamethasone / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011388:Prolactin / Q000096:biosynthesis*; D051381:Rats; D013696:Temperature; D014316:Tritium; D014407:Tumor Cells, Cultured / Q000378:metabolism
D014316:Tritium; D003907:Dexamethasone; D011388:Prolactin