CENTRO DE INVESTIGACIONES CARDIOVASCULARES "DR. HORACIO EUGENIO CINGOLANI"
Unidad Ejecutora - UE
congresos y reuniones científicas
The caMKII-dependent pathway of beta-adrenergic phosphorylation of ryanodine receptors in the intact heart increases fast calcium release kinetics and ryanodine binding in sarcoplasmic reticulum vesicles.
MUNDIÑA-WEILENMANN C, SÁNCHEZ G, FERRERO P, SAID M, VITTONE L, VALVERDE C, DONOSO P, MATTIAZZI A.
New London , estado de New Hampshire, USA
Congreso; Gordon Conference 2006; 2006
Gordon Conference 2006
There are three different phosphorylation sites at the cardiac ryanodine receptor (RyR2), identified up to now: Ser2808 (or Ser2809), Ser2815 (or Ser 2814), and Ser2030, although there is evidence that indicates the presence of CaMKII-dependent phosphorylatable residues as yet not identified (Rodríguez et al., 2003). It has been shown that Ser2815 site is phosphorylated by CaMKII (Weherens et al., 2004) and that Ser2030 is phosphorylated by PKA (Xiao, 2005, 2006), whereas there is some controversy about which is/are the kinase(s) that phosphorylate(s) Ser2809 site (Witcher et al, 1991; Rodriguez et al. 2003; Wehrens et al. 2004). Previous experiments have demonstrated that ß-adrenergic stimulation (PKA) significantly increases the maximal rate of SR Ca2+ release and speed the turn-off of release for a given ICa and SR Ca2+ load (Ginsburg & Bers, 2004). It has also been shown that beta-adrenergic stimulation phosphorylates Ser2809 (Wehrens et al., 2004, Obayashy et al., 2005) and Ser2030 (Xiao et al, 2005). However no increases in the phosphorylation of Ser2815 were found under ß-adrenergic stimulation (Wehrens et al., 2004), an intervention known to produce not only PKA but also CaMKII activation. described that Ser2815 site of RyR2 is phosphorylated by increasing stimulation rate and that this phosphorylation was associated with an increase in RyR2 Ca2+ sensitivity and open probability (Wehrens et al. Circ Res 2004). These experiments failed to show an increase in the phosphorylation of this site under β-adrenoceptor stimulation, an intervention known to produce not only PKA but also CaMKII activation. The present experiments were undertaken to explore the possibility that Ser2815 becomes phosphorylated during β-adrenoceptor stimulation and, in that case, whether this phosphorylation has a functional impact. Phosphorylation of Ser2809 was also determined. We performed experiments in the isolated perfused rat heart contracting under isovolumic conditions. After stabilization, isoproterenol (from 0.3 to 300 nM) was administered in the absence and the presence of a low concentration of calcium and nifedipine to avoid calcium influx to the cell or of the CaMKII-inhibitor KN-93 (5 μM). The results indicated that Ser2815 as well as Ser2809 site of RyR2 are dose-dependently phosphorylated by isoproterenol. At maximal isoproterenol stimulation, the inhibition of CaMKII significantly decreased Ser2815 phosphorylation without changes in the phosphorylation of Ser2809 site. CaMKII inhibition also abolished the isoproterenol-induced maximal 3H-ryanodyne binding and significantly decreased the isoproterenol-induced increase in the rate constant of fast (msec) Ca2+ release, measured by stopped flow optical techniques at a same SR Ca2+ load. The results indicate that phosphorylation of Ser2815 site of RyR2 is a main responsible for the functional effects of isoproterenol on Ca2+ release channels in the intact heart.