NPY-stimulated Ca2+ mobilization in SK-N-MC cells is enhanced after isoproterenol treatment

Neuropeptide Y (NPY) receptors in the SK-N-MC human neuroblastoma cell line couple to mobilization of intracellular Ca2+ and inhibition of adenylylcyclase. Pretreatment of SK-N-MC cells with isoproterenol enhanced the NPY-stimulated Ca2+ mobilization, mainly by increasing the maximal response to NPY. The enhancement was time-(maximal after 24 h) and concentration-dependent (maximal at 10 microM isoproterenol), blocked by the beta-adrenergic antagonist propranolol, and mimicked by forskolin. Concomitant treatment with cycloheximide prevented the enhancing effect of isoproterenol, suggesting the involvement of protein synthesis. Isoproterenol treatment did not alter the number or affinity of 125I-labeled NPY binding sites, the amount of pertussis toxin substrates, or NPY-mediated inhibition of cAMP accumulation. Similarly, isoproterenol treatment had no effect on basal intracellular Ca2+ and on Ca2+ increases elicited by carbachol, caffeine, or ionomycin. We conclude that isoproterenol treatment can sensitize NPY receptor responsiveness in a way that is specific for Ca2+ mobilization mechanisms used by this hormone.