FREQUENCY-DEPENDENT ACCELERATION OF RELAXATION (FDAR) CANNOT RELY ON PHOSPHOLAMBAN PHOSPHORYLATION

VALVERDE CA; FERRERO P; SAID M; MUNDIÑA-WEILENMANN C; VITTONE L; MATTIAZZI A

Capital Federal

Congreso; XII Meeting of the ISHR - XXII Congreso Nacional de Cardiología; 2003

Latin American Section of the International Society for Heart Research - Federación Argentina de Cardiología

Isoproterenol (Iso) induces a relaxant effect  which is dependent on the phosphorylation of phospholamban (PLB) at Ser16 and Thr17 sites. In contrast the role of PLB in FDAR is controversial. The present study reassess the issue in perfused rat hearts by comparing a similar relaxant effect (decrease in half relaxation time, t1/2) produced by 300 nM Iso or increasing stimulation frequency (from 2 to 8.5 Hz). While Iso significantly increased both Ser16 and Thr17 phosphorylations, FDAR was not associated with the phosphorylation of either sites.   Control (n=4) Iso (n=10) FDAR (n=5) t½  (Dmsec) 0 -20.6±2.3 -20.8±1.8 P-Ser16 (%) 15.4±6.2 96.8±2.0* 8.4±3.7 P-Thr17 (%) 30.4±7.9 93.6±4.4* 29.2±6.0 The results indicate that, PLB phosphorylation is not contributing to FDAR, at least in the perfused rat heart.