Extracellular ATP induces oscillations of intracellular Ca2+ and membrane potential and promotes transcription of IL-6 in macrophages

The effects of low concentrations of extracellular ATP on cytosolic Ca2+, membrane potential, and transcription of IL-6 were studied in monocyte-derived human macrophages. During inflammation or infection many cells secrete ATP. We show here that application of 10 muM ATP or 10 muM UTP induces oscillations in cytosolic Ca2+ with a frequency of approximate to12 min(-1) and oscillations in membrane potential. RT-PCR analysis showed expression of P2Y(1), P2Y(2), P2Y(11), P2X(1), P2X(4), and P2X(7) receptors, large-conductance (KCNMA1 and KCNMB1-4), and intermediate-conductance (KCNN4) Ca2+-activated K+ channels. The Ca2+ oscillations were unchanged after removal of extracellular Ca2+, indicating that they were mainly due to movements of Ca2+ between intracellular compartments. Comparison of the effects of different nucleotides suggests that the Ca2+ oscillations were elicited by activation of P2Y(2) receptors coupled to phospholipase C. Patch-clamp experiments showed that ATP induced a transient depolarization, probably mediated by activation of P2X(4) receptors, followed by membrane potential oscillations due to opening of Ca2+-activated K+ channels. We also found that 10 muM ATPgammaS increased transcription of IL-6 approximate to40-fold within 2 h. This effect was abolished by blockade of P2Y receptors with 100 muM suramin. Our results suggest that ATP released from inflamed, damaged, or metabolically impaired cells represents a danger signal that plays a major role in activating the innate immune system.