NEUROPEPTIDE-Y INHIBITS ADRENERGIC TRANSMITTER RELEASE IN CULTURED RAT SUPERIOR CERVICAL-GANGLION CELLS BY RESTRICTING THE AVAILABILITY OF CALCIUM THROUGH A PERTUSSIS-TOXIN-SENSITIVE MECHANISM

Neuropeptide Y has been reported to inhibit the release of the adrener gic transmitter from sympathetic nerves in many tissues. The purpose o f this study was to determine the mechanism of the inhibitory effect o f neuropeptide Y on the release of the adrenergic transmitter in cultu red superior cervical ganglion cells prelabeled with tritiated norepin ephrine. In cultured superior cervical ganglion cells superfused with a HEPES-buffered saline, electrical field stimulation(1 Hz, 30 pulses, 1 ms, 60 V) increased the fractional overflow of tritium. Neuropeptid e Y (50 nM) attenuated this depolarization-induced increase in transmi tter release. The nonhydrolyzable cAMP analog, 8-(4-chlorophenylthio)c yclic AMP (100 mu M) and the potassium channel blockers, tetraethylamm onium chloride (1 mM) and 4-aminopyridine (300 mu M) potentiated the e lectrically stimulated increase in fractional tritium overflow but fai led to alter the inhibitory effect of neuropeptide Y on fractional tri tium overflow. Increasing the calcium concentration in the superfusion fluid from 1.8 to 5.4 mM potentiated the electrically stimulated incr ease in fractional tritium overflow and attenuated the inhibitory effe ct of neuropeptide Y. Reduction of superfusion fluid calcium concentra tion to 0.5 mM decreased electrically stimulated fractional tritium ov erflow and augmented the inhibitory effect of NPY on release of tritiu m. The fractional release of tritium in response to the calcium ionoph ore, ionomycin, was not significantly altered by neuropeptide Y. In Fu ra-2-loaded isolated sympathetic neurites obtained from superior cervi cal ganglia explants, the depolarization-induced (54 mM KCl) increase in cytosolic calcium was attenuated by neuropeptide Y (50 nM). Pertuss is toxin (100 ng/ml for 4 h) pretreatment abolished both the neuropept ide Y-induced decrease in electrically stimulated fractional tritium o verflow and the reduction in depolarization-induced increase in cytoso lic calcium. These data suggest that NPY inhibits adrenergic transmitt er release in cultured superior cervical ganglion cells by decreasing the availability of calcium for the release process by a pertussis tox in-sensitive mechanism.