Purine and pyrimidine nucleotides activate distinct signalling pathways in PC12 cells

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Abstract
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 ∼ UTP > 2‐methylthioadenosine triphosphate (2‐MeSATP), typical of P2U. 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 [3H]tetraphenylphosphonium ([3H]TPP+) as potential‐sensitive probes, we showed that while ATP rapidly depolarized PC 12 cells in an Na+ ‐dependent manner, UTP evoked a much reduced and delayed response. The potency profile (ATP ∼ 2‐MeSATP ∼ adenosine 5′‐0‐(3thiotriphosphate) (ATPγS) ≫ UTP, α, beta;‐methyleneATP) suggested involvement of a receptor subtype distinct from P2U. Secretion of endogenous dopamine was also assessed. Those nucleotides that induced depolarization (ATP, 2‐MeSATP, ATPγS) 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 path ways. © 1995 Wily‐Liss, Inc.