Subcellular discordant alternans in cardiac myocytes: characterization and susceptibility to pharmacological RyR2 modulation.

ORLOWSKI A; MARTÍN VILA PETROFF; SOMMESE LEANDRO; CARLOS VALVERDE; GONANO LUIS; RACIOPPI, MARÍA FLORENCIA; WILLIAM LOUCH

Santiago de Chile

Congreso; Congreso de la asociación latinoamericana de ciencias fisiológicas; 2020

ALACF

Objectives: To characterize discordant calcium release in ventricular cardiomyocytes, and evaluate the impact of pharmacologicalinhibition of Ryanodine receptors (RyR2) on the occurrence and magnitude of discordance. Materials and methods: Ventricularcardiomyocytes were obtained from wistar rats (8-12 weeks old) after heart excision and enzymatic digestion. Cells were loadedwith Fluo-4 and line-scanned in a confocal microscope to detect cytosolic Ca2+. Pharmacological inhibition of RyR2 was testedwith 5 μM of both VK-II-86 and Dantrolene. Tree groups of cells (control, VK-II-86 and dantrolene) were field stimulated at 1 and5 hertz. After 1 minute at each frequency electrical pacing was stopped to record spontaneous Ca2+ release (Ca2+ waves).Results:We found previously undescribed features of subcellular discordant alternans such as its reversibility after returning to bas alpacing frequency and its instability promoted by the recruitment of out-of-phase Ca2+ release zones by its neighbors. Adiscordance index (DI) is proposed (Standard deviation of local alternans ratio) and correlated with the degree of negative staircasewith a Pearson r of -0.66 (n= 15).The equipotent RyR2 inhibition obtained with VK-II-86 and dantrolene was evident when Ca2+waves frequency was significantly reduced compared to control (ANOVA with tukey post-test). At both basal and high pacingfrequency only VK-II-86 promoted a significant increase of DI (n=14-22 per group. ANOVA with tukey post-test).Conclusions:Subcellular discordant alternans are a reversible process induced by rapid pacing and can be characterized with a Discordanceindex which correlates with transient amplitude-frequency relationship and is sensitive to pharmacological RyR2 modulation.Interestingly, differential response to VK-II-86 and dantrolene was observed, suggesting that RyR2 modulation and prevention ofCa2+ waves occurrence can be reached with normal or high chance of promoting discordant Ca2+ release.PICT 2017 nº 1297 to LG and MVP and PICT 2018-02204 to LG.