Does the velocity of SR Ca2+ refilling influence Ca2+ release refractoriness? An experimental and computational study

FELICE, JUAN IGNACIO; CELY-ORTIZ, DIANA CATALINA ALEJANDRA; VALVERDE, CARLOS ALFREDO; FEDERICO, MARILÉN; PALOMEQUE, JULIETA; WEHRENS, XANDER H T; KRANIAS, EVANGELINA GALANI; LASCANO, ELENA CATALINA; NEGRONI, JORGE ANTONIO; MATTIAZZI, RAMONA ALICIA

Philadelpfia

Congreso; American Heart Association?s Scientific Sessions 2019; 2019

American Heart Association

Each heartbeat - during which Ca2+is released from the sarcoplasmic reticulum (SR) - is followed by a refractoryperiod. Recovery from refractoriness is known as Ca2+ releaserestitution (CRR), and its alterations are potential triggers of Ca2+arrhythmias. Although the control of CRR has been associated with SR Ca2+refilling kinetics and RyR2 Ca2+ sensitivity, the relative role ofthese factors in defining CRR remains largely undefined. An intriguing point,difficult to dissect and previously neglected, is the possible independenteffect of SR Ca2+ content on CRR vs. the velocity of SR Ca2+refilling. To assess these interrogates, we used perfused mouse hearts andisolated myocytes with phospholamban (PLN) ablation (PLNKO), knock-in mice withpseudo-constitutive CaMKII phosphorylation of S2814 on RyR2 (S2814D), andS2814D mice crossed with PLN ablation mice (SDKO). In addition, a previouslyvalidated human cardiac myocyte model that mimics the experimental conditions inmouse hearts was included. The restitution of cytosolic Ca2+ (Fura2-AM) and membrane action potentials (AP, glass microelectrodes) was evaluatedwith a two-pulse (S1/S2) protocol. CRR increased as a function of the (S2-S1)coupling interval, following a single exponential curve. Experimental APrestitution did not differ among the different mouse models. In contrast, CRRwas enhanced when increasing SR Ca2+ load in both WT and S2814Dmyocytes. Moreover, for a given SR Ca2+ load, CRR was accelerated inS2814D myocytes vs. WT, but not in PLNKO and SDKO myocytes. These results suggestthat the velocity of SR Ca2+ reuptake does not affect CRR. However,when the compensatory decrease in RyR2 expression produced by PLN ablation wascorrected, the model revealed that the velocity of refilling does accelerateCRR independently of SR Ca2+ load. In conclusion, RyR2 activity, SR Ca2+load and the velocity of SR Ca2+ refilling are main and independentdeterminants of CRR.