title: Inhibition of receptor-mediated calcium responses by corticotrophin-releasing hormone in the CATH.a cell line.
abstract: A region of the brain believed to be important in the CNS response to stress is the locus coeruleus, the predominant site of noradrenergic cell bodies. Corticotrophin releasing hormone (CRH) is the primary hypothalamic releasing hormone responsible for the activation of the pituitary-adrenal axis in response to stress and, in this study, we employed a locus coeruleus-like cell line, CATH.a, to investigate the modulation of receptor signalling pathways by CRH. Pituitary adenylyl cyclase-activating polypeptide (PACAP) (10 nM), vasoactive intestinal peptide (VIP) (1 microM) and carbachol (1 mM) produced transient increases in intracellular [Ca2+]. The inhibition of the carbachol (1 mM) response by CRH was concentration-dependent (EC50 = 154 +/- 1.8 nM). Calcium responses to sub-maximally effective concentrations of PACAP (5 nM), VIP (400 nM) and carbachol (1 mM) were abolished by prior exposure to CRH (1 microM). At the concentrations employed, CRH and VIP both substantially increased intracellular [3H]-cyclic AMP accumulation. The adenylyl cyclase activator forskolin (10 microM) was also effective at eliminating the agonist-induced calcium responses. Incubation with the cell permeant cyclic AMP analogue dibutyryl cyclic AMP (dbcAMP) (1 mM), an activator of protein kinase A (PKA), for 12 min prior to agonist exposure similarly abolished the intracellular calcium response to carbachol. Carbachol increased [3H]-inositol phosphate ([3H]-IP) accumulation to a maximum of 2.4 +/- 0.11-fold basal (EC50 = 6.75 +/- 0.26 microM). PACAP produced a much greater accumulation (19.9 +/- 2.1 fold basal; EC50 = 24 nM). In the presence of forskolin (10 microM), neither carbachol- nor PACAP-induced [3H]-IP accumulation was significantly different from in its absence. These results demonstrate that CRH inhibits receptor-mediated intracellular calcium responses in a locus coeruleus-like cell line possibly via activation of PKA. This modulation could be important in controlling neuronal function in vivo in stressful situations in which the levels of CRH are increased in the locus coeruleus.
authors: School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, UK.
authors: R A
authors: RA
authors: Bundey
authors: D A
authors: DA
authors: Kendall
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D006868:Hydrolysis; D008125:Locus Coeruleus / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D016015:Logistic Models; D051379:Mice; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects*; D009479:Neuropeptides / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
chemical_list: C495402:Adcyap1 protein, mouse; D015220:Calcium Channels; D009479:Neuropeptides; D010716:Phosphatidylinositols; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D014660:Vasoactive Intestinal Peptide; D002217:Carbachol; D003346:Corticotropin-Releasing Hormone; D014446:Tyrosine 3-Monooxygenase