Corticosteroid modulation of signal transduction in the CATH.a cell line

Noradrenergic neuronal networks originating in the locus coeruleus have been implicated in the stress response. In order to study this system in vitro, we have employed a locus coeruleus-like cell line, CATH.a, and have determined the effect of dexamethasone on receptor-mediated second messenger responses. The CATH.a cell line produced increases in intracellular cyclic AMP conversion in response to corticotrophin-releasing factor (EC50 = 6.93 +/- 1.26 nM, maximum conversion = 4.11 +/- 0.20%) and vasoactive intestinal polypeptide (EC50 = 240 +/- 40 nM, maximum conversion = 8.92 +/- 1.24%). Forskolin (10 microM) increased conversion from 0.48 +/- 0.05 to 6.39 +/- 0.38%. The alpha 2-adrenoceptor agonist 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK14304) inhibited the forskolin response with an IC50 of 6.76 +/- 0.11 nM. Carbachol increased total 3H-labelled inositol phosphate accumulation to a maximum of 3.01 +/- 0.79 fold basal (EC50 = 7.94 +/- 0.14 microM). Bradykinin produced a maximum 1.81 +/- 0.05 fold basal stimulation of phosphoinositide hydrolysis (EC50 = 9.12 +/- 0.16 nM). Both carbachol and bradykinin increased intracellular Ca2+ concentration probably via a combination of mobilisation of intracellular stores and gating of extracellular Ca2+. Incubation for 24 h with the glucocorticoid receptor agonist, dexamethasone (1 microM), significantly potentiated the receptor-mediated phosphoinositide responses to all the agents tested; however, of the receptor-mediated increases in cyclic AMP conversion, only the vasoactive intestinal polypeptide response was potentiated. These results show that the CATH.a cell line displays some of the properties expected of locus coeruleus neurons and that glucocorticoid receptor stimulation selectively modulates receptor-mediated increases in second messenger formation.