InsP3-Induced Ca2+ Release in Atrial Myocytes

Abstract

The contribution and significance of InsP3-induced Ca2+ release (IP3ICR) in cardiac excitation-contraction coupling (ECC) is still a matter of debate. IP3ICR may be involved and targeted during cellular remodeling of ECC under pathophysiological stress. Here we intend to characterize IP3ICR and the interplay of InsP3Rs and RyRs in atrial myocytes. We hypothesized a functional crosstalk and/or cooperativity between both SR-Ca2+ release channels, e.g. IP3ICR may trigger or facilitate Ca2+-induced Ca2+ release (CICR) via RyR activation and/or RyR sensitization. InsP3-induced Ca2+ release events were activated by rapid superfusion with 20 μM InsP3 in permeabilized atrial myocytes acutely isolated from mice hearts. Separation between CICR (Ca2+ sparks) and IP3ICR (Ca2+ puffs) was performed by pharmacological interventions using tetracaine and 2-APB. SR-Ca2+ release events were recorded using high-speed 2D confocal imaging. Data were analyzed using an IDL software based algorithm. Direct InsP3R activation leads to an increase of 23% in the number of Ca2+ release events compared to the number of spontaneous events under control. 2D Ca2+ release event analysis revealed more Ca2+ events with smaller amplitudes (0.75, p=0.01) and increased FWHM (1.14, p=0.02) in the presence of InsP3 compared to spontaneous Ca2+ sparks associated with RyRs openings. RyRs block (1 mM tetracaine) and/or InsP3Rs inhibition (2 μM 2-APB) shift InsP3 triggered local Ca2+ release events towards events with lower amplitude and higher FWHM which was not observed in the absence of InsP3. This suggests that InsP3 evoked SR-Ca2+ release events do not exist as singular InsP3 evoked Ca2+ release events but as Ca2+ release events that derive from both RyRs and InsP3Rs and suggesting that IP3ICR may be linked to CICR in atrial cells. Supported by SNF.