The effects of neuropeptide Y (NPY; 1-36) and NPY fragment (16-36) on nicotinic currents (IACh) and voltage-dependent calcium currents (ICa) were studied in bovine chromaffin cells using the whole-cell patch-clamp technique. The peak amplitude of inward nicotinic currents was markedly depressed by both NPY (1-36) and NPY (16-36). In contrast, ICa was unaffected by either NPY (1-36) or NPY (16-36). Both pertussis toxin pretreatment and including GDP [beta-S] in the patch pipette solution completely abolished the inhibitory effect of NPY on IACh. It is concluded that inhibition of IACh probably represents the mechanism by which NPY decreases catecholamine release from adrenal medulla. This effect appears to be mediated by a G-protein-coupled Y2 receptor.