Regulation of gonadotropin receptors on cultured porcine Leydig and Sertoli cells: effect of potassium depletion.
We have examined the role of the NaK-ATPase pump activity on the ligand-induced down-regulation of gonadotropin receptors in cultured porcine Leydig and Sertoli cells. In both cells, inhibition of the NaK pump by ouabain produced a depletion of intracellular K+ levels (ID50, 10(-7) M) after a lag period of about 8 h. In the absence of ligand, the number of FSH receptors in ouabain-treated Sertoli cells was unaffected or slightly reduced, whereas a 2-fold increase in the number of human CG (hCG)/LH receptors with small changes in the binding affinity was observed in Leydig cells treated by ouabain. The effect of ouabain was dose dependent. Differences were also observed in the down-regulation process of gonadotropin receptors in ouabain-treated cells. The hCG-induced receptor loss in Leydig cells was completely reversed by ouabain whereas the drug had no effect on ligand-induced loss of FSH receptors in Sertoli cells. Similar results were observed when the cells were incubated in K+-free medium. Kinetics studies with labeled hCG have shown that ouabain treatment slows down significantly the rate of [125I]iodo-hCG internalization (t 1/2, 18 h; control cells, t 1/2, 6 h), but had no effect on the degradation of internalized hormone. The internalization of receptor-bound [125I]iodo-hCG was also reduced when Leydig cells were incubated in K+-free medium, but was restored when this medium was supplemented with rubidium. The influence of the NaK pump on the receptor regulation of a ligand common to both types of cells, such as epidermal growth factor, was studied under the same experimental conditions. Neither ouabain nor K+-free medium were able to prevent the epidermal growth factor-induced reduction of receptor levels in Leydig and Sertoli cells. Thus, it appears that modulation of ligand-induced receptor loss by depletion of cellular K+ levels is not dependent on the cell type, but on the ligand-receptor complex. The data also show a striking difference in the dynamics of gonadotropin-receptor interaction of two structurally related hormones.
M
M
Bernier
B
B
Laferrere
C
C
Jaillard
M
M
Clerget
J M
JM
Saez
D000818:Animals; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000378:metabolism / Q000494:pharmacology; D066246:ErbB Receptors; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D007473:Ion Channels / Q000502:physiology; D007985:Leydig Cells / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011962:Receptors, FSH; D011974:Receptors, LH; D012708:Sertoli Cells / Q000187:drug effects / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013552:Swine
D006063:Chorionic Gonadotropin; D007473:Ion Channels; D011956:Receptors, Cell Surface; D011962:Receptors, FSH; D011974:Receptors, LH; C041222:iodo-chorionic gonadotropin; D010042:Ouabain; D005640:Follicle Stimulating Hormone; D066246:ErbB Receptors; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium