Adenosine triphosphate (ATP) is assumed to be involved in the regulation of
many extracellular signaling systems including calcium wave propagation. S
o far all supportive evidence is indirect, such as monitoring changes in in
tracellular calcium on application of extracellular ATP or off-site measure
ment of ATP from superfusates. Furthermore, the causal relationships among
the various signaling agents are still unclear. A novel chemiluminescence d
ynamic imaging method was developed to monitor ATP release from living biol
ogical cells. The assay has linear response over 3 orders of magnitude for
fixed concentrations of enzyme and cofactors, with a correlation coefficien
t of 0.999. The detectability of ATP is down to 10(-8) M at millisecond exp
osure times with an intensified charge-coupled device camera. The direct im
aging of ATP waves in astrocyte cultures was performed together with Fluo-3
-Ca imaging at millisecond temporal resolution and micrometer-scale spatial
resolution. We discovered that extracellular ATP mediates intercellular ca
lcium wave propagation, but surprisingly, release and propagation of ATP ar
e not calcium dependent. Therefore, ATP rather than Ca or IP3 is the primar
y intercellular signaling messenger.