UTP evokes noradrenaline release from rat sympathetic neurons by activation of protein kinase C

The pathway involved in UTP-evoked noradrenaline release was investigated i n cultures of rat superior cervical ganglia. Northern blots revealed an age -related increase in levels of mRNA for P2Y6 receptors in cultures obtained at postnatal days 1 and 5, respectively, but no change in transcripts for P2Y1 and P2Y2. Likewise, UTP-evoked overflow of previously incorporated [H- 3]noradrenaline was six-fold higher in neurons obtained at postanatal day 5 . Various protein kinase C inhibitors diminished UTP-, but not electrically , induced tritium overflow by > 70%, as did down-regulation of protein kina se C by 24 h exposure to phorbol ester. beta -Phorbol-12,13-dibutyrate and dioctanoylglycerol caused concentration-dependent increases in [H-3] outflo w of up to 6% of total radioactivity, and the secretagogue actions of these agents were reduced in the presence of protein kinase C inhibitors and in neurons pretreated with phorbol ester. Overflow evoked by dioctanoylglycero l was attenuated in the absence of extracellular Ca2+ and in the presence o f tetrodotoxin or Cd2+. In addition to triggering tritium overflow, UTP red uced currents through muscarinic K+ channels which, however, were not affec ted by phorbol esters. This action of UTP was not altered by protein kinase C inhibitors. These results indicate that P2Y6 receptors mediate UTP-evoke d noradrenaline release from rat sympathetic neurons via activation of prot ein kinase C, but not inhibition of K-M channels.