ATP release during cell swelling activates a Ca2+-dependent Cl− current by autocrine mechanism in mouse hippocampal microglia

Abstract

Microglia cells, resident immune cells of the brain, survey brain parenchyma by dynamically extending and retracting their processes. Cl− channels, activated in the cellular response to stretch/swelling, take part in several functions deeply connected with microglia physiology, including cell shape changes, proliferation, differentiation and migration. However, the molecular identity and functional properties of these Cl− channels are largely unknown. We investigated the properties of swelling-activated currents in microglial from acute hippocampal slices of Cx3cr1 +/GFP mice by whole-cell patch-clamp and imaging techniques. The exposure of cells to a mild hypotonic medium, caused an outward rectifying current, developing in 5–10 minutes and reverting upon stimulus washout. This current, required for microglia ability to extend processes towards a damage signal, was carried mainly by Cl− ions and dependent on intracellular Ca2+. Moreover, it involved swelling-induced ATP release. We identified a purine-dependent mechanism, likely constituting an amplification pathway of current activation: under hypotonic conditions, ATP release triggered the Ca2+-dependent activation of anionic channels by autocrine purine receptors stimulation. Our study on native microglia describes for the first time the functional properties of stretch/swelling-activated currents, representing a key element in microglia ability to monitor the brain parenchyma.

Dissection of P2X4 and P2X7 Receptor Current Components in BV-2 Microglia

“…The activation of microglia cells depends on extracellular ATP, which can be released from damaged tissue [ 3 ]. Alternatively, microglia cells can themselves release ATP to promote inflammation [ 4 , 8 , 9 ]. VRAC inhibitors protected the brain from injury in rodent models of transient and permanent cerebral ischemia, implying a major pathological significance of VRACs in stroke [ 88 ].…”

“…The DAMPs include ATP which is released from damaged or inflamed tissue [ 7 ]. Microglia cells not only are activated by ATP, but also secrete ATP themselves by mechanisms that have not yet been fully elucidated [ 4 , 8 , 9 ]. Receptors for extracellular ATP are the G-protein coupled P2Y and the ionotropic P2X purinergic receptors [ 10 , 11 ].…”

NGF steers microglia toward a neuroprotective phenotype

“…Our analysis shows that the receptor‐mediated signaling activated by NGF in microglia regulates a number of physiological activities of these cells, even triggering an outward rectifying membrane current. Although the identity of this current remains to be determined, the value of its reversal potential leads to propose that this NGF‐induced current may be subserved also by chloride channels (Murana et al, ).…”

“…Although the identity of this current remains to be determined, the value of its reversal potential leads to propose that this NGF-induced current may be subserved also by chloride channels (Murana et al, 2017).…”

Disruption of the Microglial ADP Receptor P2Y13 Enhances Adult Hippocampal Neurogenesis

“…In addition, constitutive cellular ATP release (Lazarowski et al, 2011 ) could tonically activate microglial P2Y 13 Rs and attenuate neurogenesis. Microglial release of ATP could induce an autocrine loop (Murana et al, 2017 ) of ATP release and P2Y 13 R activation. The interstitial concentration of ATP in living rat brain (striatum) of 40 nM (Melani et al, 2012 ) would be—after hydrolysis to ADP—in the range of the EC 50 value of the P2Y 13 R (Communi et al, 2001 ).…”