Activity-dependent adenosine release may be linked to activation of Na(+)-K(+) ATPase: an in vitro rat study

In the brain, extracellular adenosine increases as a result of neuronal activity. The mechanisms by which this occurs are only incompletely understood. Here we investigate the hypothesis that the Na(+) influxes associated with neuronal signalling activate the Na(+)-K(+) ATPase which, by consuming ATP, generates intracellular adenosine that is then released via transporters. By measuring adenosine release directly with microelectrode biosensors, we have demonstrated that AMPA-receptor evoked adenosine release in basal forebrain and cortex depends on extracellular Na(+). We have simultaneously imaged intracellular Na(+) and measured adenosine release. The accumulation of intracellular Na(+) during AMPA receptor activation preceded adenosine release by some 90 s. By removing extracellular Ca(2+), and thus preventing indiscriminate neuronal activation, we used ouabain to test the role of the Na(+)-K(+) ATPase in the release of adenosine. Under conditions which caused a Na(+) influx, brief applications of ouabain increased the accumulation of intracellular Na(+) but conversely rapidly reduced extracellular adenosine levels. In addition, ouabain greatly reduced the amount of adenosine released during application of AMPA. Our data therefore suggest that activity of the Na(+)-K(+) ATPase is directly linked to the efflux of adenosine and could provide a universal mechanism that couples adenosine release to neuronal activity. The Na(+)-K(+) ATPase-dependent adenosine efflux is likely to provide adenosine-mediated activity-dependent negative feedback that will be important in many diverse functional contexts including the regulation of sleep.