Automated syringe pump

Mice were anesthetized by i.p. injection of avertin (2,2,2-tribromoethanol, Sigma–Aldrich) in 2% solution at a dose of 400 mg kg^-1 bodyweight and placed on a controlled heating pad (Föhr Medical Instruments, Seeheim-Ober Beerbach, Germany) in supine position. Additional doses of avertin (each 10% of the initial dose) were applied during experiments if appropriate to maintain depth of anesthesia. A miniature pressure-volume catheter (model SPR-839, Millar Instruments, Houston, TX, United States) was inserted via the right carotid artery and placed in the left ventricle. Increasing doses of dobutamine were administered into the cannulated left external jugular vein using an automated syringe pump (B. Braun, Melsungen, Germany). Data were recorded using the MPVS-400 system (Millar Instruments) and Chart5 software (ADInstruments, Bella Vista, NSW, Australia). At the end of experiments, animals were euthanized by avertin overdose, and hearts were excised, weighed, and stored at -80°C until further examination. Hemodynamic data were analyzed using Chart5 software (ADInstruments) and PVAN software (Millar Instruments).

Mice were anesthetized with isoflurane (∼1.2% v/v) and nitrous oxide (∼66% v/v) while being placed on a warmed pad in supine position. Needle electrodes were attached to obtain limb leads (Einthoven) and augmented limb leads (Goldberger). ECGs were recorded and analyzed electronically using PowerLab hardware and LabChart Pro software (ADInstruments, Bella Vista, Australia). Where required by the experimental protocol, a tube catheter was inserted into the left external jugular vein and drugs, i.e., the β₁-adrenoceptor antagonist (class II antiarrhythmic) esmolol (Baxter, Unterschleißheim, Germany) 10 mg/kg bw or the Na⁺-channel blocker (class Ic antiarrhythmic) flecainide (MEDA Pharma, Bad Homburg, Germany) 5 mg/kg bw, were administered intravenously using an automated syringe pump (B. Braun, Melsungen, Germany). After invasive procedures, animals were euthanized by CO₂ inhalation without having regained consciousness. Hearts were excised, photographed, weighed, and stored at -80°C until further analysis.