ATP‐induced ATP release from astrocytes

Abstract

Propagation of interastrocyte Ca 2+waves is mediated by diffusion of extracellular adenosine triphosphate (ATP), and may require regenerative release of ATP. The ability of ATP to initiate release of intracellular ATP was assessed by labeling adenine nucleotide pools in astrocyte cultures with 14 C‐adenine. The 14 C‐purines released during exposure to ATP were then identified by thin‐layer chromatography. ATP treatment caused a five‐fold increase in release of 14 C‐ATP but not 14 C‐ADP or 14 C‐AMP, indicating selectivity for release of ATP. Other P2 receptor agonists also caused significant 14 C‐ATP release, and the P2 receptor antagonists suramin, reactive blue‐2 and pyridoxalphosphate‐6‐azo(benzene‐2,4‐disulfonic acid) (PPADS) inhibited ATP‐induced 14 C‐ATP release to varying degrees, suggesting the involvement of a P2 receptor. ATP‐induced 14 C‐ATP release was not affected by chelation of intracellular Ca 2+with BAPTA‐AM, or by blockers of Ca 2+release from intracellular stores or of extracellular Ca 2+influx, suggesting a Ca 2+‐independent response. ATP‐induced 14 C‐ATP release was significantly inhibited by non‐selective anion channel blockers but not by blockers of ATP‐binding cassette proteins, gap junction hemichannels, or vesicular exocytosis. Release of adenine nucleotides induced by 0 Ca 2+was, in contrast, not selective for ATP, and was susceptible to inhibition by gap junction blockers. These findings indicate that astrocytes are capable of ATP‐induced ATP release and support a role for regenerative ATP release in glial Ca 2+wave propagation.