UTP- and ATP-triggered transmitter release from rat sympathetic neurones via separate receptors

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Abstract
In rat cultured sympathetic neurones, UDP, UTP and ATP at micromolar concentrations triggered Ca2+-dependent and tetrodotoxin-sensitive [3H]-noradrenaline release. The overflow evoked by UTP or ATP was similar at 100 μmol 1−1, the concentration used in all subsequent experiments. Pre-exposure of the neurones to 100 μmol 1−1 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 μmol 1−1 pyridoxal-5″-phosphate or 30 μmol 1−1 suramin, the secretory response to ATP was reduced, but the effect of UTP was unaltered. Zn2+ (10 μmol 1−1) 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.

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