Extracellular ATP induces oscillations of intracellular [Ca.sup.2+] and membrane potential and promotes transcription of IL-6 in macrophages

The effects of low concentrations of extracellular ATP on cytosolic [Ca.sup.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 [micro]M ATP or 10 [micro]M UTP induces oscillations in cytosolic [Ca.sup.2+] with a frequency of [approximately equal to] 12 [min.sup.-1] and oscillations in membrane potential. RT-PCR analysis showed expression of P2[Y.sub.1], P2[Y.sub.2], P2[Y.sub.11], P2[X.sub.1], P2[X.sub.4], and P2[X.sub.7] receptors, large-conductance (KCNMA1 and KCNMB1-4), and intermediate-conductance (KCNN4) [Ca.sup.2+]- activated [K.sup.+] channels. The [Ca.sup.2+] oscillations were unchanged after removal of extracellular [Ca.sup.2+], indicating that they were mainly due to movements of [Ca.sup.2+] between intracellular compartments. Comparison of the effects of different nucleotides suggests that the [Ca.sup.2+] oscillations were elicited by activation of P2[Y.sub.2] receptors coupled to phospholipase C. Patch-clamp experiments showed that ATP induced a transient depolarization, probably mediated by activation of P2[X.sub.4] receptors, followed by membrane potential oscillations due to opening of [Ca.sup.2+]- activated [K.sup.+] channels. We also found that 10 [micro]M ATP[gamma]S increased transcription of IL-6 [aproximately equal to] 40-fold within 2 h. This effect was abolished by blockade of P2Y receptors with 100 [micro]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.