Effects of endothelin-1 on its receptor concentration and thymidine incorporation in calf adrenal zona glomerulosa cells: a comparative study with phorbol esters.
Endothelin (ET-1) is a 21-amino acid peptide with potent vasopressor and vasoconstrictive properties. Specific, high affinity receptors for ET-1 have been found in the adrenal gland. The stimulation by ET-1 of aldosterone secretion in cultured calf zona glomerulosa cells was shown to depend on the serum used for culturing and was not related to the growth-promoting effects of serum or the response to another secretagogue, such as angiotensin-II. In this study, binding of [125I]ET-1 to crude membrane preparations from calf adrenal cortex slices showed that ET-1 binding was greater in the outer slices, corresponding to the zona glomerulosa, than in inner slices, corresponding to the zona fasciculata. ET-1 stimulated aldosterone, but not cortisol, biosynthesis. Adrenal zona glomerulosa preincubated with ET-1 resulted in homologous down-regulation. Since ET-1 action involves activation of protein kinase-C (PKC), we studied the effect of a phorbol ester (PMA) on the down-regulation of ET-1 receptors. PMA decreased the number of cell surface receptors, and its effect was prevented by pretreatment with the PKC inhibitors H-7 and sphyngosine. Agonist-mediated down-regulation could not be blocked by pretreatment with PKC inhibitors, suggesting that PKC is involved in phorbol ester-mediated, but not agonist-mediated down-regulation of ET-1 receptors. Both effectors increased the endocytosis rate constant as well as the steady state cytosolic membrane-bound ratio for ET-1 receptors, suggesting that the decrease in the number of cell surface receptors is at least partially due to an increased internalization of the hormone-receptor complex. ET-1 and PMA decreased the incorporation of [3H]thymidine into calf zona glomerulosa cell cultures. We conclude that ET-1 and PMA have similar effects on glomerulosa cells, producing down-regulation of ET-1 receptors and an antimitogenic effect, but these actions are through different mechanisms.
Cozza
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EN
Department of Internal Medicine, University of South Florida Health Sciences Center, Tampa.
Gomez-Sanchez
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CE
D000450:Aldosterone / Q000378:metabolism; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003470:Culture Media; D004261:DNA Replication / Q000187:drug effects*; D015536:Down-Regulation; D004705:Endocytosis; D016232:Endothelins; D004730:Endothelium, Vascular / Q000502:physiology*; D006854:Hydrocortisone / Q000378:metabolism; D010455:Peptides / Q000378:metabolism / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D017466:Receptors, Endothelin; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013936:Thymidine / Q000378:metabolism; D015384:Zona Glomerulosa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D003470:Culture Media; D016232:Endothelins; D010455:Peptides; D011956:Receptors, Cell Surface; D017466:Receptors, Endothelin; D000804:Angiotensin II; D000450:Aldosterone; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D013936:Thymidine; D006854:Hydrocortisone