Stretch‐induced Ca²⁺ independent ATP release in hippocampal astrocytes

Abstract

Astrocytic ATP release is essential for brain functions such as synaptic long-term potentiation for learning and memory. However, whether and how ATP is released via exocytosis remains hotly debated. All previous studies of non-vesicular ATP release have used indirect assays. By contrast, two recent studies report vesicular ATP release using more direct assays. In the present study, using patch clamped 'ATP-sniffer cells', we re-investigated astrocytic ATP release at single-vesicle resolution in hippocampal astrocytes. Following an 'on-cell-like' mechanical stimulus of a single astrocyte, a Ca independent single large non-quantal ATP release occurred, in contrast to the Ca -dependent multiple small quantal ATP release in a chromaffin cell. The mechanical stimulation-induced ATP release from an astrocyte was inhibited by either exposure to a selective antagonist or genetic knockdown of P2X7 receptor channels. Functional P2X7 channels were expressed in astrocytes in hippocampal brain slices. Thus, in addition to small quantal ATP release, larger non-quantal ATP release depends on P2X7 channels in astrocytes.

Differential Co-release of Two Neurotransmitters from a Vesicle Fusion Pore in Mammalian Adrenal Chromaffin Cells

“…This is consistent with the finding that the signal duration in fast-scan cyclic voltammetry is $7 times longer than that of amperometry (Wang et al, 2014b). It is known that the P2X4-ATPsniffer is capable of determining the relative sizes of quantal ATP release events during an ACC recording (Xiong et al, 2018).…”

Ca2+-Dependent and Ca2+-Independent ATP Release in Astrocytes

“…It was our original goal to record quantal ATP release in cultured hippocampal astrocytes using ATP-sniffer cells. To our surprise, with three independent assays of lysosomal exocytosis, our real-time sniffer recordings clearly denied ATP release by Ca 2+ -dependent lysosomal exocytosis (Xiong et al, 2018 ). Instead, following a gentle membrane stretch, Ca 2+ -independent non-vesicular ATP release occurred in the cultured astrocytes (Xiong et al, 2018 ).…”

“…To our surprise, with three independent assays of lysosomal exocytosis, our real-time sniffer recordings clearly denied ATP release by Ca 2+ -dependent lysosomal exocytosis (Xiong et al, 2018 ). Instead, following a gentle membrane stretch, Ca 2+ -independent non-vesicular ATP release occurred in the cultured astrocytes (Xiong et al, 2018 ). In contrast to the quantal spikes of ATP release in chromaffin cells, the Mechanically-induced ATP Release from Astrocytes (MARA) displays a single spike with distinct kinetic characteristics.…”

“…The abundant ATP is an emergency signal for the neural immune system that recruits and activates microglia in the ATP “hot-spots” and promotes disease. All data adapted from Xiong et al ( 2018 ), except B adapted from Lalo et al ( 2014 ). All data with reproduction permission from the original publishers.…”

Stimulus‐dependent modifications in astrocyte‐derived extracellular vesicle cargo regulate neuronal excitability

“…ATP is a potent inducer of EV shedding in several cell types, including microglia and astrocytes (Bianco et al, 2005(Bianco et al, , 2009Takenouchi et al, 2015). In brain, ATP can be co-released from neurons with other neurotransmitters (Edwards, Gibb, & Colquhoun, 1992;Silinsky, Gerzanich, & Vanner, 1992;Sperlagh, Kittel, Lajtha, & Vizi, 1995), and from astrocytes in response to glutamate, mechanical stretch, activation of toll-like receptor 3, and glucocorticoids (Beckel et al, 2018;Guthrie et al, 1999;Koyanagi et al, 2016;Queiroz, Gebicke-Haerter, Schobert, Starke, & von Kügelgen, 1997;Xiong et al, 2018). Extracellular ATP signals by binding to P2 receptors that include ionotropic P2X (P2X1−7) and metabotropic P2Y receptors (P2Y1, 2, 4, 6, 11-14;reviewed in Burnstock, 2007).…”