Frequency-Dependent Acceleration of Relaxation (FDAR

Frequency-Dependent Acceleration of
Relaxation (FDAR) Cannot Rely
on Phospholamban Phosphorylation.
Valverde C., Ferrero P., Said M.,
Mundiña-Weilenmann C.,
Vittone L., Mattiazzi A.
Centro de Investigaciones Cardiovasculares,
La Plata, Buenos Aires, Argentina.
Isoproterenol (Iso) induces a relaxant effect which is dependent on the phosphorylation of phospholamban
(PLB) at Ser [16] and Thr [17] sites. In contrast the role of PLB in FDAR is controversial. The present study
reassesses 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 Ser [16] and Thr [17] phosphorylations, FDAR was not associated with the
phosphorylation of either sites.
The results indicate that, PLB phosphorylation is not contributing to FDAR, at least in the perfused rat heart.
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