Interaction between alpha 2-adrenergic and NPY receptor pathways in human erythroleukemia cells.

Neuropeptide Y (NPY) appears to be a transmitter of the sympathetic nervous system, and its actions are similar to those of alpha 2-adrenergic receptor stimulation. In human erythroleukemia (HEL) cells, both NPY and epinephrine (acting through alpha 2-adrenergic receptors) inhibit adenylate cyclase and mobilize intracellular Ca++. We investigated possible interactions between NPY and epinephrine. In radioligand binding assays NPY did not alter antagonist or agonist binding to alpha 2-adrenergic receptors. NPY and epinephrine did not act synergistically to elevate intracellular Ca++. Neither agent alone, nor both together, affected the intracellular pH of HEL cells. Preincubation with NPY (like epinephrine) redistributed the alpha 2-adrenergic receptors away from the cell surface and into a sequestered pool.