Measurements of VAMP2 and SYP levels in retinal lysates were performed by surface plasmon resonance using antibodies

directed against VAMP2 (Cl 69.1) and SYP (Cl 7.2; Synaptic Systems) coupled to a CM3 sensor chip of a Biacore 3000 system. A nonimmune IgG (Jackson Immunoresearch) was used to reduce nonspecific binding as described (Ferracci et al., 2005). Frozen retinae were sonicated (3 × 2 s, 40W) in 300 μl of 10 mM HEPES/NaOH (pH 7.4), 0.32 M sucrose, 5 mM DTT as described (Marconi et al., 2008) and 10,000 × g lysate supernatants were incubated at 37°C during 30 min. Samples were diluted in analysis buffer (50 mM Tris/HCl [pH 7.4], 0.4 M NaCl) and the surface plasmon resonance signal was measured 20 s MDV3100 after the end of each injection (20 μl/min). We used a fluorometric enzyme assay based on the Amplex Red Glutamic Acid kit (Invitrogen) to visualize glutamate release from

acutely isolated Müller cells, which were identified by their unique morphology. Retinae were incubated in papain (0.2 mg/ml; Roche Molecular Biochemicals) for 30 min at 37°C in the dark in Ca2+- and Mg2+-free extracellular solution (140 mM NaCl, 3 mM KCl, 10 mM HEPES, 11 mM glucose [pH 7.4]), which was supplemented with glutamine (0.25 mM), glutamate Selleckchem Alectinib (0.5 mM), methionine sulfoximine (5 mM, Sigma) to block glutamine synthetase, and a photolabile calcium chelator (O-nitrophenyl ethylene glycol tetraacetic acid acetoxymethyl; NP-EGTA, 10μM; Invitrogen). After several washes with extracellular solution, to which MgCl2 (1 mM) and CaCl2 (2 mM) were added, retinae were triturated in extracellular solution containing the components of the Amplex Red Glutamic Acid kit (100 μM Amplex Red reagent, 0.5 U/ml horse radish peroxidase, 0.16 U/ml L-glutamate oxidase,

1.0 U/ml L-glutamate-pyruvate transaminase, 400 μM L-alanine), NP-EGTA (10 μM), methionine sulfoximine (200 μM), and D, L-threo-beta-benzyloxyaspartate (200 μM) to block glial glutamate uptake. The cell suspension was mixed with 1% agarose and from incubated for 15 min in the recording chamber at 37°C. In some experiments, bafilomycin A1 (200 nM, Biozol) was added. Resorufin fluorescence was imaged by confocal laser microscopy (LSM510 Meta, 100×/1.3 Plan-Neofluar oil, Zeiss; 543 nm helium-neon laser, 585 nm long pass filter, pinhole maximally open) above Müller cell endfeet. Calcium transients were induced by four UV pulses (351 nm/364 nm Enterprise UV Laser, 500 ms at maximal intensity) to release calcium from NP-EGTA. Control experiments using fluo-4/AM (488 nm argon laser; 505–550 nm band-pass filter) confirmed that each cell tested (15 out of 15) showed UV-induced calcium transients. Peak amplitudes were calculated as difference between mean fluorescence intensity across four time points acquired before and after the UV pulses.