UTP-TRIGGERED AND ATP-TRIGGERED TRANSMITTER RELEASE FROM RAT SYMPATHETIC NEURONS VIA SEPARATE RECEPTORS

In rat cultured sympathetic neurones, UDP, UTP and ATP at micromolar concentrations triggered Ca2+-dependent and tetrodotoxin-sensitive [H-3]-noradrenaline release. The overflow evoked by UTP or ATP was similar at 100 mu mol l(-1), the concentration used in all subsequent experiments. Pre-exposure of the neurones to 100 mu mol l(-1) UTP significantly reduced ensuing secretory effects of UTP but not of ATP. Conversely, pre-exposure to ATP diminished the overflow due to ATP but not that due to UTP. In the presence of 10 mu mol l(-1) pyridoxal-5'-phosphate or 30 mu mol l(-1) suramin, the secretory response to ATP was reduced, but the effect of UTP was unaltered. Zn2+(10 mu mol l(-1)) reduced the overflow triggered by UTP, but increased the overflow due to ATP. These results indicate the presence of separate receptors for pyrimidine nucleotides and for purine nucleotides which both trigger transmitter release.