PERTUSSIS TOXIN-INSENSITIVE CALCIUM INFLUX MEDIATED BY NEUROPEPTIDE Y-2 RECEPTORS IN A HUMAN NEUROBLASTOMA CELL-LINE

Stimulation of neuropeptide Y (NPY) Y-2 receptors induced an intracellular free Ca2+ ([Ca2+](i)) increase in a human neuroblastoma cell line, CHP-234. When NPY in a Ca2+-free solution was applied, this increase was abolished. Depolarization with high KC1 evoked no response, suggesting that the responses were not mediated by voltage-gated Ca2+ channels. There was no evidence that the NPY response consisted of a capacitative Ca2+ entry sensitive to internal Ca2+ store levels. The [Ca2+](i) elevation was diminished by Ni2+, a blocker of Ca2+ entry. Mn2+ induced a quench of the fura-2 fluorescence, which ceased promptly upon the removal of NPY, indicating that Ca2+ entry was linked tightly to receptor activation. Although thapsigargin- and ryanodine-sensitive Ca2+ stores were present, NPY induced responses were not impaired by pretreatment with either drug. Further-more, NPY had no effect on the thapsigargin sensitive store. Pertussis toxin did not affect the NPY-stimulated [Ca2+](i) increase, although it abolished the NPY-dependent inhibition of cAMP production. It is concluded that the Y-2 receptors couple directly to receptor-operated Ca2+ channels without the involvement of intracellular Ca2+ stores. The results also indicate that Y-2 receptors can activate both pertussis toxin-sensitive and -insensitive mechanisms in the same cell.