ИСТИНА

Most of ectothermic animals unable to cope with acute temperature changes due to heart failure. It has been suggested that heart failure occurs as a result of atrioventricular (AV) or ventricular conduction blockade. However, partially terrestrial anurans are well known poikilotherms which heart well tolerate fast thermal challenges in wide temperature diapason. Electrophysiological mechanisms underlying preservation of heart performance in anurans are not completely elucidated. In this study, standard surface ECG was recorded in anesthetized frog Rana temporaria after double autonomic blockade at various temperatures (2-25C, n=18) and RR, PQ intervals were calculated (Powergraph-3.3 software). Optical mapping approach was applied to evaluate AV and ventricular conduction under varied temperatures (4-25C). Optical action potentials from multicellular isolated, perfused, di-4-ANEPPS stained and blebbistatin treated preparations (n=6) consisting of atrial and ventricular heart regions with minimally manipulated AV ring were collected with use of CCD camera (WuTech Inst.) and analyzed (RedShirtImaging software). Frogs demonstrated normal ECG in diapason from 2 to 25C. Both RR and PQ intervals revealed similar temperature dependence, Q10 coefficients. Temperature alteration never caused AV blocks, however, cooling resulted in AV delay increasing (210±22 at 25C and 740±102 ms at 2C). Identical (associated with interatrial septum ridges) pathways of conduction in frog AV ring were observed under all tested temperatures. Excitation in ventricle was conducted without blocks or disturbances in 4-25C range. Temperature alteration has significantly weaker influence on ventricle then on AV conduction. Thus, maintenance of AV and ventricular conduction may underlie thermal tolerance of a anurans heart.