Expression of serotonin7 receptor and coupling of ectopic receptors to protein kinase A and ionic currents in adrenocorticotropin-independent macronodular adrenal hyperplasia causing Cushing's syndrome

Context: In ACTH-independent macronodular adrenal hyperplasia (AIMAH) causing Cushing's syndrome, cortisol secretion is controlled by illegitimate membrane receptors. Objective: The aim of the present study was to characterize the pharmacological properties and the transduction mechanisms of illegitimate receptors, i.e. receptors for serotonin (5-HT), gastric inhibitory polypeptide ( GIP), and LH/human chorionic gonadotropin (hCG), expressed by AIMAH tissues to evaluate the role of ectopic receptors in the physiopathology of Cushing's syndrome. Design: We used in vitro studies on cultured adrenal hyperplasia cells. Setting: The setting was a university research laboratory. Patients: AIMAH tissues (H1-H3) were removed from three patients previously screened for illegitimate receptors. Main Outcome Measure(s): The main outcome measures were steroidogenic and electrical activities of cultured adrenal hyperplasia cells. Results: In vitro studies showed that the corticotropic effect of 5-HT was mediated by ectopic 5-HT7 receptors in H1 and H2. GIP and hCG-stimulated cortisol production via activation of cAMP-dependent protein kinase A in H2. On the contrary, the protein kinase A inhibitor H-89 did not affect hCG-induced cortisol production in H3. Activation of 5-HT7 or GIP receptors enhanced T-type calcium current in H1 or H2 and H3, respectively. In addition, GIP reduced the amplitude of transient and sustained potassium currents in H2. Conversely, hCG did not modify T-type calcium current in H3. Conclusions: These data show that, besides their coupling to the cAMP pathway, illegitimate adrenal receptors can activate additional transduction mechanisms, including modulation of membrane channels.