Propionic acid

Flies were reared and maintained at 25 ˚C, 60% humidity with a 12 h: 12 h light-dark circle unless otherwise noted. All flies used in this study were out-crossed to the wild-type Canton-S (wtcs) background and maintained on standard cornmeal agar medium except for the irradiation assay with antibiotics (see below). The standard food recipe was as follows: 105 g dextrose, 7.5 g agar, 26 g yeast, 50 g cornmeal, and 1 L purified H₂O were mixed and boiled for 30 min with constant agitation, and 1.7 g Tegosept (Sigma Aldrich, St. Louis, MO, USA) dissolved in 8.5 ml 95% ethanol and 1.9 ml propionic acid (99%, Mallinckrodt Baker) was added. wtcs, UAS-NaChBac, and Tdc2-Gal4 flies were gifts from Dr. Yi Rao in Peking University. UAS-dTrpA1 and UAS-Kir2.1 transgenic flies were from the Bloomington Drosophila Stock Center, and out-crossed to the wtcs background.

2,2’-Dipyridyl disulfate, 4-nitro-7-piperazino-2,1,3-benzoxadiazole, 5,6-diamino-2,4-hydroxypyrimidine sulfate, pentobarbital sodium, and triphenyl phosphine were purchased from Tokyo Kasei Kogyo (Tokyo, Japan). Ammonia was obtained from Showa Chemical (Tokyo, Japan), and ammonium chloride was purchased from Kanto Chemical (Tokyo, Japan). A bicinchonic acid (BCA) Protein Assay kit was obtained from Thermo Fisher Scientific (Waltham, USA). Citric acid monohydrate and sodium hydroxide were purchased from Nacalai Tesque (Kyoto, Japan). Lithium D-lactate, lithium L-lactate, paraformaldehyde, and methylglyoxal were obtained from Sigma Chemical (St. Louis, USA). High-performance liquid chromatography (HPLC)-grade acetonitrile was obtained from Merck (Darmstade, Germany). HPLC-grade methanol and propionic acid were purchased from Mallinckrodt Baker (Phillipsburg, USA). Saikosaponin C was obtained from Wako Pure Chemical (Osaka, Japan). Triflouroacetic acid was purchased from Riedel-de Haën (Seelze, Germany).