Astrocyte calcium waves propagate proximally by gap junction and distally by extracellular diffusion of ATP released from volume-regulated anion channels

Wave-like propagation of [Ca2+](i) increases is a remarkable intercellular communication characteristic in astrocyte networks, intercalating neural circuits and vasculature. Mechanically-induced [Ca2+](i) increases and their subsequent propagation to neighboring astrocytes in culture is a classical model of astrocyte calcium wave and is known to be mediated by gap junction and extracellular ATP, but the role of each pathway remains unclear. Pharmacologic analysis of time-dependent distribution of [Ca2+](i)revealed three distinct [Ca2+](i) increases, the largest being in stimulated cells independent of extracellular Ca2+ and inositol 1,4,5-trisphosphate-induced Ca2+ release. In addition, persistent [Ca2+](i) increases were found to propagate rapidly via gap junctions in the proximal region, and transient [Ca2+](i) increases were found to propagate slowly via extracellular ATP in the distal region. Simultaneous imaging of astrocyte [Ca2+](i) and extracellular ATP, the latter of which was measured by an ATP sniffing cell, revealed that ATP was released within the proximal region by volume-regulated anion channel in a [Ca2+](i) independent manner. This detailed analysis of a classical model is the first to address the different contributions of two major pathways of calcium waves, gap junctions and extracellular ATP.