|
pubmed:abstractText |
We have further characterized angiotensin receptors on bovine adrenal fasciculata cells whose presence was previously demonstrated by the intrinsic agonistic activity of angiotensin II (AII), dex-Asp1-AII, angiotensin I (AI), and des-ASp1-AI on steroidogenesis. The specific binding of AII and des-Asp1-AII labeled with 125I to dispersed bovine fasciculata cells was studied. For both peptides, a single class of binding sites accounted for the data with a mean (+/- SEM) Ka value of 0.23 +/- 0.123 X 10(8) liters/mol for AII and 0.68 X 10(8) liters/mol for des-Asp1-AII. The concentration at which unlabeled AII and des-Asp1-AII displaced 50% of the tracers (Kd) was similar to that at which they induced half-maximal stimulation of steroidogenesis (Kact). For AI and des-Asp1-AI, Kd greater than Kact. Analogs of AII or des-Asp1-AII with antagonistic properties upon steroidogenesis competed also with binding of the tracers. Corticotropin (ACTH) did not inhibit binding. Although ACTH stimulated the formation of cyclic AMP, none of the angiotensins with intrinsic activity did so. Calcium, but not potassium, appeared to potentiate the steroidogenic activity of AII. These data suggest that there is a single class of receptors for angiotensins and analogs in zona fasciculata. These receptors show characteristics that differentiate them from ACTH receptors in zona fasciculata or angiotensin receptors in zona glomerulosa cells.
|
