P2Y-mediated Ca2+ response is spatiotemporally graded and synchronized in sensory neurons: a two-photon photolysis...

ATP is thought to be an initiator and modulator of noxious pain sensation. We employed two-photon photolysis to apply ATP locally and transiently, thus mimicking ATP release upon cell damage or exocytosis. Using this technique, an increase in intracellular Ca2+ concentration ([Ca2+]i) was induced via P2Y receptors in individual sensory neurons, or in a neurite region. The ATP-induced [Ca2+]i rise was attenuated by applications of either a phospholipase C inhibitor, or inhibitors for IP3 or ryanodine receptors. These results indicate that intracellular Ca2+ stores play a major role in contributing to the increase in [Ca2+]i. Spatiotemporal analysis revealed that local and transient applications of ATP increased [Ca2+]i by release from intracellular stores, but in a unique, graded, and synchronized manner. 1) As the duration of local ATP application was prolonged, the latency decreased and the magnitude of the [Ca2+]i rise increased; 2) The time course of the rising phase of the [Ca2+]i response to ATP was essentially the same over the cell body, once [Ca2+]i had started to rise. It is anticipated that sensory responses may be modulated variably, depending on the spatiotemporal characteristics of the ATP-related [Ca2+]i profile.