Изменения внеклеточно регистрируемых потенциалов действия изолированного сердца крысы при развитии стрептозотоцинового диабета

Abstract

Left ventricles (LV) of isolated hearts of the control rats (n = 7) and rats injected with streptozotocin (STZ; n = 21) were studied on the four-week post-injection term using 5-µm tip (O.D.) glass extracellular microelectrodes. STZ-rats that maintained hyperglycemia by the time of the study (random glucose > 11 mM; n = 3) were designated as diabetic animals (diabetes mellitus group; STZ-DM). Remaining STZ-rats (n = 18) were designated as normoglycemic rats (STZ-NG group). In control and in STZ-rat hearts two main types of sinus rhythm action potentials (AP) of epicardial ventricular myocytes could be recorded: signals characterized by a single (AP1) or double negative peaks (AP2). Respective time parameters of AP1 (rise time, and 50% and 90% decay times (T50 and T90) not differed between studied groups of rats. However, T50 of AP2 of LV myocytes of STZ-NG and STZ-DM rats were statistically significantly longer than T50 of AP2 recorded in control rat hearts. Furthermore, in 28% of STZ-NG and in 67% of STZ-DM rat hearts additional type of AP (AP3) featuring a complex, multi-peak negative phase and prominent positive phase of after-hyperpolarization were recorded. Appearance of AP3 was associated with a proportional decrease in the relative frequency of AP2 recordings (from 80-85% to 55-60% of all recordings). Frequency of AP1 recordings remained stable, 15-20% in all experiments in all groups of rats. Tentatively, observed in this study modulation in electrical activity of ventricular myocytes of STZ-rat hearts results from structure-functional changes in organization of the T-system of these myocytes. Regardless of validity of this suggestion, it is important that changes in electrogenesis of cardiomyocytes develop fast (1 month) not only in STZ-DM rats, but also in hearts of STZ-rats with normal or moderately increased blood glucose levels, which may be considered as the state equivalent to the state of early prediabetes.