Determinants of Ca2+ Release Restitution: Insights from Genetically Altered Animals and Mathematical Modeling

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

JOURNAL OF GENERAL PHYSIOLOGY

ROCKEFELLER UNIV PRESS

Lugar: New York; Año: 2020

0022-1295

Each heartbeat is followed by a refractory period. Recovery from refractoriness is known as Ca2+ release restitution (CRR) and its alterations are potential triggers of Ca2+ arrhythmias. Although the control of CRR has been associated with sarcoplasmic reticulum (SR) Ca2+ load and ryanodine receptors (RyR2) Ca2+ sensitivity, the relative role of some of the determinants of CRR remains largely undefined. An intriguing point, difficult to dissect and previously neglected, is the possible independent effect of SR Ca2+ content vs. the velocity of SR Ca2+ refilling, on CRR. To assess these interrogates, we used isolated myocytes with phospholamban (PLN) ablation (PLNKO), knock-in mice with pseudo-constitutive CaMKII phosphorylation of RyR2 S2814 (S2814D), S2814D crossed with PLNKO mice (SDKO) and a previously validated human cardiac myocyte model. Restitution of cytosolic Ca2+ (Fura-2 AM) and L-type calcium current (ICaL, patch-clamp) was evaluated with a two-pulse (S1/S2) protocol. CRR and ICaL restitution increased as a function of the (S2-S1) coupling interval, following an exponential curve. When SR Ca2+ load was increased by increasing extracellular [Ca2+] from 2.0 to 4.0 mM, CRR and ICaL restitution were enhanced, suggesting that ICaL restitution may contribute to the faster CRR observed at 4.0 mM [Ca2+]. In contrast, ICaL restitution did not differ among the different mouse models. For a given SR Ca2+ load, CRR was accelerated in S2814D myocytes vs. WT, but not in PLNKO and SDKO myocytes vs. WT and S2814D, respectively. The model mimics all experimental data. Moreover, when the PLN ablation-induced-decrease in RyR2 expression was corrected, the model revealed that CRR was accelerated in PLNKO and SDKO vs. WT and S2814D myocytes, respectively, suggesting that the velocity of refilling does enhance CRR independently of SR Ca2+ load.