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.