Recombinant mouse fgf23

Animals were maintained at controlled temperature (23–25 °C) on a 12-h light/dark cycle with ad libitum access to water and a standard diet (ROD14, Altromin Spezialfutter GmbH & Co. KG). Animals were housed in groups of 4 per cage of 553 cm² by 20.8 cm depth (polysulfone cage type II L, SODISPAN) with standard wood chip (ECO-PURE 7 Chips, Tapvei®).
Adult 14-week-old male C57BL/6 J mice (Charles River Laboratories International Inc.) were used to study the effect of FGF23 on heart rhythm by a single-dose intraperitoneal injection of recombinant mouse FGF23 (40 μg/kg) (R&D Systems) during ECG recording.

Human atrial fibroblasts were purchased from Lonza Research Laboratory (Walkersville, MD, USA). As described previously [22 (link)], cells were seeded on uncoated culture discs as monolayers and cultured in Dulbecco’s modified Eagle medium (Thermo Fisher Scientific, Loughborough, UK) containing 10% fetal bovine serum (Hyclone, Logan, UT, USA) and 100 U/mL penicillin–streptomycin (Thermo Fisher Scientific, Loughborough, Gibco, UK) in a humidified atmosphere of 5% CO₂ at 37 °C. Cells used in this study were from passages 4–6 to avoid possible variations in cellular function. Cardiac fibroblasts treated without and with recombinant mouse FGF-23 (1, 5 or 25 ng/mL; R&D Systems, Abingdon, UK) in the presence and absence of an FGF receptor 1 antagonist (PD166866, 1 μM; Sigma, St. Louis, MO, USA), a free Ca²⁺ chelator (EGTA, 1 mM; Sigma), or a PLC inhibitor (U73122, 1 μM; Abcam, Cambridge, UK) for 48 h were harvested for further analysis.