Threonine-17 phosphorylation of phospholamban: a key determinant of frequency-dependent increase of cardiac contractility.
Multiple studies have shown that phospholamban (PLN) plays a key role in regulation of frequency-dependent increase of cardiac contraction, a hallmark of the contractile reserve in myocardium. However, the mechanisms underlying this relationship remain elusive. Phosphorylation of PLN occurs on residues: serine-16 (Ser(16)) and threonine-17 (Thr(17)) in vivo. In isolated wild-type cardiomyocytes, we found that increases of stimulation frequency from 0.5 to 5 Hz were associated with increased Thr(17) phosphorylation of PLN and cardiac contractility. To further delineate the role of PLN phosphorylation in the frequency-dependent increases of cardiac function, three transgenic mouse models, expressing wild-type, Ser16Ala (S16A), or Thr17Ala (T17A) mutant PLN in the null background were generated. Transgenic lines expressing similar levels of wild-type or mutant PLN were selected and isolated cardiomyocytes were paced from 0.5 to 5 Hz. Upon increases in pacing frequency, the fractional shortening (FS) and rates of contraction (+dL/dt) and relaxation (-dL/dt) increased in wild-type and S16A mutant PLN cardiomyocytes. In contrast, in myocytes expressing the T17A mutant PLN, there were no increases in FS and +/-dL/dt upon increasing the frequency of stimulation. The time to 50% peak shortening (TTP(50)) and to 50% relaxation (TTR(50)) were also abbreviated to a much higher extent (two-fold) in wild-type and S16A mutant compared to T17A mutant PLN cardiomyocytes. These results indicate that Thr(17) phosphorylation of PLN is the major contributor to frequency-dependent increases of contractile and relaxation parameters in mouse cardiomyocytes, although some increases in these parameters occur even in the absence of PLN phosphorylation. Thus, the positive force-frequency relationship in cardiomyocytes is mechanistically and mainly related to PLN phosphorylation.
Zhao
Wen
W
Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0575, USA.
Uehara
Yoshiki
Y
Chu
Guoxiang
G
Song
Qiujing
Q
Qian
Jiang
J
Young
Karen
K
Kranias
Evangelia G
EG
D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D066298:In Vitro Techniques; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D009200:Myocardial Contraction / Q000235:genetics / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*; D010766:Phosphorylation; D013912:Threonine / Q000235:genetics / Q000378:metabolism*; D000099211:Phospholamban
D002135:Calcium-Binding Proteins; D013912:Threonine; D000099211:Phospholamban