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

Abstract

The effects of low concentrations of extracellular ATP on cytosolic Ca 2؉ , 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 M ATP or 10 M UTP induces oscillations in cytosolic Ca 2؉ with a frequency of Ϸ12 min ؊1 and oscillations in membrane potential. RT-PCR analysis showed expression of P2Y 1, P2Y2, P2Y11, P2X1, P2X 4, and P2X7 receptors, large-conductance (KCNMA1 and KCNMB1-4), and intermediate-conductance (KCNN4) Ca 2؉ -activated K ؉ channels. The Ca 2؉ oscillations were unchanged after removal of extracellular Ca 2؉ , indicating that they were mainly due to movements of Ca 2؉ between intracellular compartments. Comparison of the effects of different nucleotides suggests that the Ca 2؉ oscillations were elicited by activation of P2Y2 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 Ca 2؉ -activated K ؉ channels. We also found that 10 M ATP␥S increased transcription of IL-6 Ϸ40-fold within 2 h. This effect was abolished by blockade of P2Y receptors with 100 M 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.

The role of purinergic signaling in the liver and in transplantation: effects of extracellular nucleotides on hepatic graft vascular injury, rejection and metabolism

“…Polymorphisms of P2X7 have been associated with decreased killing of Mycobacteria (129)(130)(131). Furthermore secretion of interleukin-6 possibly by stimulation of P2X4 receptors activates innate immunity (132). In one report, liver injury by ATP was attenuated by administration of gadolinium chloride, which depletes Kupffer cells; Suramin a P2 receptor antagonist has comparable effect.…”

Interleukin-6 regulates the zinc transporter Zip14 in liver and contributes to the hypozincemia of the acute-phase response

“…The sequelae of events include ATP leakage from inflamed cells, changes in intracellular Ca 2ϩ , and membrane potential, which lead to enhanced IL-6 transcription in macrophages (26). Of note in this context is that the Zip14 promoter has response elements for numerous physiologic͞ immune mediators, suggesting other factors are involved in the regulation of Zip14 in specific cell types.…”

Schistosome apyrase SmATPDase1, but not SmATPDase2, hydrolyses exogenous ATP and ADP

“…These signals, collectively called damage-associated molecular patterns (DAMPs), indicate tissue damage to the host and can initiate primary immune responses. Extracellular nucleotides such as ATP are known to function as DAMPs by acting as endogenous tissue-derived signalling molecules that contribute to inflammation and immunity [5,6]. Extracellular ATP can act as a proinflammatory immunomediator by acting on multiple immunological effector cell types including neutrophils, macrophages, dendritic cells, and lymphocytes (reviewed in [5,7,8]).…”

“…Extracellular nucleotides such as ATP are known to function as DAMPs by acting as endogenous tissue-derived signalling molecules that contribute to inflammation and immunity [5,6]. Extracellular ATP can act as a proinflammatory immunomediator by acting on multiple immunological effector cell types including neutrophils, macrophages, dendritic cells, and lymphocytes (reviewed in [5,7,8]). It has been hypothesized that schistosome ectoenzymes can degrade exogenous ATP so as to impede host immune cell activation in the vicinity of the worms [9], and it has long been known that schistosome tegumental extracts do possess ATP and ADP hydrolyzing activity [10,11].…”