Experimental model
The study conformed to the Guide for the Care and Use of Laboratory Animals, 8th Edition published by the National Academies Press (US), 2011, the guidelines from Directive 2010/63/EU of the European Parliament on the protection of animals used for scientific purposes, and was approved by the ethical committee of the Institute of Physiology of the Komi Science Centre, Ural Branch of Russian Academy of Sciences. The experiments were carried out on 98 rabbits of both sexes of the Chinchilla breed aged 6-8 months. For the induction of type 1 diabetes mellitus, 72 rabbits were given a single dose of alloxan at a dose of 120 mg / kg body mass by intravenous injection. Venous plasma glucose concentration was measured once a week with an OneTouch glucometer (LifeScan). Subsequently, 55 animals became diabetic, and DM did not develop in 17 rabbits (fasting venous plasma glucose level being <7.0 mmol/L). As a result, the electrophysiological measurements were carried out in 55 rabbits (28 males) with uncontrolled DM and 43 (22 males) control animals (the animals that have not been administered alloxan and animals that have not developed diabetes after administration of alloxan). DM duration was from 28 to 76 days [median 42 days, interquartile range (IQR) 36-54 days].
For electrophysiological study, the rabbits were anaesthetized by intramuscular injection of zoletil (15 mg/kg body mass). The animals were intubated and mechanically ventilated, and midsternal thoracotomy was performed. The temperature of the heart was maintained at 37-38 °C by irrigation with warm saline and heating ambient room air. A 64-lead sock array (3.0-5.0 mm inter-electrode distance) was placed on ventricular epicardium. Recordings of unipolar electrograms with reference to Wilson‘s central terminal were done under spontaneous sinus rhythm by means of a custom-designed mapping system (16 bits; bandwidth 0.05-1000.0 Hz; sampling rate 4000 Hz). After recording, the left anterior descending coronary artery was ligated to develop ischemia for 15 min followed by 15 min period of reperfusion provided by loosening the ligature. To assess arrhythmogenicity we used arrhythmia induction by burst stimulation (600 impulses per minute, twice diastolic threshold) of the left ventricular apex at the end of ischemic exposure and reperfusion.