Neuropeptide Y mobilizes Ca2+ and inhibits adenylate cyclase in human erythroleukemia cells

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Abstract
Neuropeptide Y (NPY), a peptide often coreleased with catecholamines, appears to be an important component of the sympathetic nervous system, but little is known about the molecular basis of its action. We introduce here human erythroleukemia (HEL) cells as a new model system for studies of NPY action. NPY inhibited adenosine 3,5'-cyclic monophosphate (cAMP) accumulation in HEL cells with a 50% effective concentration (EC50) of 3 nM. Additionally NPY increased intracellular Ca2+, as assessed by fura-2 fluorescence, with a similar EC50. Pretreatment with pertussis toxin blocked both responses, suggesting the involvement of one or more G proteins. Chelating extracellular Ca2+ with EGTA did not reduce the Ca2+ signal, demonstrating mobilization from intracellular stores rather than influx. Experiments with various agents demonstrated that the Ca2+ mobilization was not secondary to lowering of cAMP levels, formation of arachidonic acid products, or Na+-H+ exchange. Ca2+ mobilization also did not appear to be associated with inositol phosphate generation. In conclusion, we demonstrate for the first time that NPY, in addition to inhibiting adenylate cyclase, also can elevate intracellular Ca2+. HEL cells should prove useful in further studies of the molecular basis of NPY action.