PURINE AND PYRIMIDINE NUCLEOTIDES ACTIVATE DISTINCT SIGNALING PATHWAYS IN PC12 CELLS

The role of extracellular nucleotides in intracellular signalling and neurosecretion was assessed in PC12 cells. Activation of phospholipase C and increased [Ca2+](i) were mediated by purinoceptors with an agonist potency profile, ATP similar to UTP > 2-methylthioadenosine triphosphate (2-MeSATP), typical of P-2U. ATP also evoked a rapid acidification followed by a more gradual alkalinization (measured with 2',7'-biscarboxyethyl-5(6) -carboxyfluorescein (BCECF)), while UTP induced only a gradual alkalinization. The amiloride analogue 5-(N-ethyl-N-isopropyl)amiloride (EIPA) attenuated the alkalinization phase suggesting activation of the Na+/H+ exchanger by ATP and UTP, Using bisoxonol and [H-3]tetraphenylphosphonium ([3H]TPP+) as potential-sensitive probes, we showed that while ATP rapidly depolarized PC12 cells in an Na+-dependent manner, UTP evoked a much reduced and delayed response. The potency profile (ATP similar to 2-MeSATP similar to adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) >> UTP, alpha,beta-methyl-eneATP) suggested involvement of a receptor subtype distinct from P-2U. Secretion of endogenous dopamine was also assessed, Those nucleotides that induced depolarization (ATP, 2-MeSATP, ATP gamma S) were also the most potent secretagogues. UTP was ineffective. Our results suggest that ATP stimulates distinct purinoceptor subtypes and induces neurosecretion through the activation of multiple signalling pathways. (C) 1995 Wiley-Liss, Inc.