Subcellular distribution and early signalling events of P2X7 receptors from mouse cerebellar granule neurons

The subcellular distribution and early signalling events of P2X7 receptors were studied in mouse cerebellar granule neurons. Whole-cell patch-clamp recordings evidenced inwardly directed non-desensitizing currents following adenosine 5′-triphosphate (ATP; 600µM) or 2′-3′-o-(4-benzoylbenzoyl)-adenosine 5′-triphosphate (BzATP; 100µM) administration to cells bathed in a medium with no-added divalent cations (Ca2+ and Mg2+). Nucleotide-activated currents were inhibited by superfusion of 2.5mM Ca2+, 1.2mM Mg2+ or 100nM Brilliant Blue G (BBG), hence indicating the expression of ionotropic P2X7 receptors. Fura-2 calcium imaging showed [Ca2+]i elevations in response to ATP or BzATP at the somas and at a small number of axodendritic regions of granule neurons. Differential sensitivity of these [Ca2+]i increases to three different P2X7 receptor antagonists (100nM BBG, 10μM 4-[(2S)-2-[(5-isoquinolinylsulfonyl)methylamino]-3-oxo-3-(4-phenyl-1-piperazinyl)propyl] phenyl isoquinolinesulfonic acid ester, KN-62, and 1μM 3-(5-(2,3-dichlorophenyl)-1H-tetrazol-1-yl)methyl pyridine hydrochloride hydrate, A-438079) revealed that P2X7 receptors are co-expressed with different P2Y receptors along the plasmalemma of granule neurons. Finally, experiments with the fluorescent dye YO-PRO-1 indicated that prolonged stimulation of P2X7 receptors does not lead to the opening of a membrane pore permeable to large cations. Altogether, our results emphasise the expression of functional P2X7 receptors at both the axodendritic and somatic levels in mouse cerebellar granule neurons, and favour the notion that P2X7 receptors might function in a subcellular localisation-specific manner: presynaptically, by controlling glutamate release, and on the cell somas, by supporting granule neuron survival against glutamate excytotoxicity.