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 agon ist potency profile, ATP similar to UTP > 2-methylthioadenosine tripho sphate (2-MeSATP), typical of P-2U. ATP also evoked a rapid acidificat ion followed by a more gradual alkalinization (measured with 2',7'-bis carboxyethyl-5(6) -carboxyfluorescein (BCECF)), while UTP induced only a gradual alkalinization. The amiloride analogue 5-(N-ethyl-N-isoprop yl)amiloride (EIPA) attenuated the alkalinization phase suggesting act ivation 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+-depend ent manner, UTP evoked a much reduced and delayed response. The potenc y profile (ATP similar to 2-MeSATP similar to adenosine 5'-O-(3-thiotr iphosphate) (ATP gamma S) >> UTP, alpha,beta-methyl-eneATP) suggested involvement of a receptor subtype distinct from P-2U. Secretion of end ogenous dopamine was also assessed, Those nucleotides that induced dep olarization (ATP, 2-MeSATP, ATP gamma S) were also the most potent sec retagogues. UTP was ineffective. Our results suggest that ATP stimulat es distinct purinoceptor subtypes and induces neurosecretion through t he activation of multiple signalling pathways. (C) 1995 Wiley-Liss, In c.