Phospholamban-to-SERCA2 ratio controls the force-frequency relationship

1999 ◽  
Vol 276 (3) ◽  
pp. H779-H785 ◽  
Author(s):  
Markus Meyer ◽  
Wolfgang F. Bluhm ◽  
Huaping He ◽  
Steven R. Post ◽  
Frank J. Giordano ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Transgenic Mice ◽  
Cardiac Myocytes ◽  
Cardiac Contractility ◽  
Adult Rabbit ◽  
Force Frequency ◽  
Papillary Muscles ◽  
Inhibitory Protein ◽  
Frequency Relationship ◽  
Myocyte Contractility

The force-frequency relationship (FFR) describes the frequency-dependent potentiation of cardiac contractility. The interaction of the sarcoplasmic reticulum Ca2+-adenosinetriphosphatase (SERCA2) with its inhibitory protein phospholamban (PLB) might be involved in the control of the FFR. The FFR was analyzed in two systems in which the PLB-to-SERCA2 ratio was modulated. Adult rabbit cardiac myocytes were transduced with adenovirus encoding for SERCA2, PLB, and β-galactosidase (control). After 3 days, the relative PLB/SERCA2 values were significantly different between groups (SERCA2, 0.5; control, 1.0; PLB, 4.5). SERCA2 overexpression shortened relaxation by 23% relative to control, whereas PLB prolonged relaxation by 39% and reduced contractility by 47% (0.1 Hz). When the stimulation frequency was increased to 1.5 Hz, myocyte contractility was increased by 30% in control myocytes. PLB-overexpressing myocytes showed an augmented positive FFR (+78%), whereas SERCA2-transduced myocytes displayed a negative FFR (−15%). A more negative FFR was also found in papillary muscles from SERCA2 transgenic mice. These findings demonstrate that the ratio of phospholamban to SERCA2 is an important component in the control of the FFR.

scholarly journals Regulation of cardiac myocyte contractility by phospholemman: Na+/Ca2+ exchange versus Na+-K+-ATPase

2008 ◽  
Vol 295 (4) ◽  
pp. H1615-H1625 ◽  
Author(s):  
Jianliang Song ◽  
Xue-Qian Zhang ◽  
JuFang Wang ◽  
Ellina Cheskis ◽  
Tung O. Chan ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Myocytes ◽  
Cardiac Myocyte ◽  
Fluorescent Protein ◽  
Surface Membrane ◽  
Cardiac Contractility ◽  
Normal Surface ◽  
Plasmic Reticulum ◽  
Green Fluorescent ◽  
Myocyte Contractility

Phospholemman (PLM) regulates cardiac Na+/Ca2+ exchanger (NCX1) and Na+-K+-ATPase in cardiac myocytes. PLM, when phosphorylated at Ser68, disinhibits Na+-K+-ATPase but inhibits NCX1. PLM regulates cardiac contractility by modulating Na+-K+-ATPase and/or NCX1. In this study, we first demonstrated that adult mouse cardiac myocytes cultured for 48 h had normal surface membrane areas, t-tubules, and NCX1 and sarco(endo)plasmic reticulum Ca2+-ATPase levels, and retained near normal contractility, but α1-subunit of Na+-K+-ATPase was slightly decreased. Differences in contractility between myocytes isolated from wild-type (WT) and PLM knockout (KO) hearts were preserved after 48 h of culture. Infection with adenovirus expressing green fluorescent protein (GFP) did not affect contractility at 48 h. When WT PLM was overexpressed in PLM KO myocytes, contractility and cytosolic Ca2+ concentration ([Ca2+]i) transients reverted back to those observed in cultured WT myocytes. Both Na+-K+-ATPase current ( Ipump) and Na+/Ca2+ exchange current ( INaCa) in PLM KO myocytes rescued with WT PLM were depressed compared with PLM KO myocytes. Overexpressing the PLMS68E mutant (phosphomimetic) in PLM KO myocytes resulted in the suppression of INaCa but had no effect on Ipump. Contractility, [Ca2+]i transient amplitudes, and sarcoplasmic reticulum Ca2+ contents in PLM KO myocytes overexpressing the PLMS68E mutant were depressed compared with PLM KO myocytes overexpressing GFP. Overexpressing the PLMS68A mutant (mimicking unphosphorylated PLM) in PLM KO myocytes had no effect on INaCa but decreased Ipump. Contractility, [Ca2+]i transient amplitudes, and sarcoplasmic reticulum Ca2+ contents in PLM KO myocytes overexpressing the S68A mutant were similar to PLM KO myocytes overexpressing GFP. We conclude that at the single-myocyte level, PLM affects cardiac contractility and [Ca2+]i homeostasis primarily by its direct inhibitory effects on Na+/Ca2+ exchange.

Force-frequency relationship and rest potentiation in papillary muscles of Siberian ground squirrel in the period of preparation to hibernation

2006 ◽  
Vol 407 (1) ◽  
pp. 74-76 ◽  
Author(s):  
O. V. Nakipova ◽  
L. A. Andreeva ◽  
N. A. Chumaeva ◽  
N. M. Zakharova ◽  
N. I. Kukushkin ◽  
...  
Keyword(s):  
Ground Squirrel ◽  
Force Frequency ◽  
Papillary Muscles ◽  
Frequency Relationship

Abstract 2375: Regulation of Cardiac Myocyte Contractility by Phospholemman

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Jianliang Song ◽  
Xue-Qian Zhang ◽  
JuFang Wang ◽  
Ellina Cheskis ◽  
Tung O Chan ◽  
...  
Keyword(s):  
Cardiac Myocytes ◽  
Cardiac Myocyte ◽  
Adult Mouse ◽  
Surface Membrane ◽  
Cardiac Contractility ◽  
Wild Type ◽  
Inhibitory Effects ◽  
Normal Surface ◽  
Membrane Area ◽  
Myocyte Contractility

Phospholemman (PLM) regulates cardiac contractility by modulating Na + /Ca 2+ exchanger (NCX1) and/or Na + -K + -ATPase activities. PLM, when phosphorylated at serine68, disinhibits Na + -K + -ATPase but inhibits NCX1. In this study, we first demonstrated that adult mouse cardiac myocytes cultured for 48 hours had normal surface membrane area and t-tubule appearance, and exhibited near normal contractility. Contractile differences between wild-type (WT) and PLM knockout (KO) myocytes were preserved after 48h of culture. Infection with adenovirus overexpressing GFP did not affect contractility at 48h. When WT PLM was overexpressed in PLM-KO myocytes, part of PLM was phosphorylated, both Na + -K + -ATPase current (I pump ) and Na + /Ca 2+ exchange current (I NaCa ) were depressed, and contractility and [Ca 2+ ] i transients reverted back to those observed in cultured WT myocytes. Overexpressing PLMS68E mutant (phosphomimetic) in PLM-KO myocytes resulted in suppression of I NaCa but no effect on I pump . Contractility and [Ca 2+ ] i transient amplitudes in PLM-KO myocytes overexpressing PLMS68E mutant were depressed when compared to PLM-KO myocytes overexpressing GFP. Overexpressing PLMS68A mutant (mimicking unphosphorylated PLM) in PLM-KO myocytes had no effects on I NaCa but decreased I pump . Contractility and [Ca 2+ ] i transient amplitudes in PLM-KO myocytes overexpressing S68A mutant were similar to PLM-KO myocytes overexpressing GFP. Neither WT PLM nor its mutants had any effect on SR Ca 2+ uptake in KO myocytes. We conclude that at the single myocyte level, PLM affects cardiac contractility and [Ca 2+ ] i homeostasis primarily by its direct inhibitory effects on Na + /Ca 2+ exchange.

scholarly journals Phospholamban: a major determinant of the cardiac force-frequency relationship

2000 ◽  
Vol 278 (1) ◽  
pp. H249-H255 ◽  
Author(s):  
Wolfgang F. Bluhm ◽  
Evangelia G. Kranias ◽  
Wolfgang H. Dillmann ◽  
Markus Meyer
Keyword(s):  
Cyclopiazonic Acid ◽  
Left Ventricular ◽  
Major Determinant ◽  
Force Frequency ◽  
Papillary Muscles ◽  
Wild Type ◽  
Plasmic Reticulum ◽  
Frequency Potentiation ◽  
Frequency Relationship

The cardiac force-frequency relationship has been known for over a century, yet its mechanisms have eluded thorough understanding. We investigated the hypothesis that phospholamban, a potent regulator of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA), determines the cardiac force-frequency relationship. Isolated left ventricular papillary muscles from wild-type (WT) and phospholamban knockout (KO) mice were stimulated at 2 to 6 Hz. The force-frequency relationship was positive in WT but negative in KO muscles, i.e., it was inverted by ablation of phospholamban ( P < 0.01, n = 6 mice). From 2 to 6 Hz, relaxation accelerated considerably (by 10 ms) in WT muscles but only minimally (by 2 ms) in KO muscles (WT vs. KO: P < 0.0001, n = 6). To show that the lack of frequency potentiation in KO muscles was not explained by the almost maximal basal contractility, twitch duration was prolonged in six KO muscles with the SERCA inhibitor cyclopiazonic acid to WT values. Relaxation still failed to accelerate with increased frequency. In conclusion, our results clearly identify phospholamban as a major determinant of the cardiac force-frequency relationship.

scholarly journals Phospholamban overexpression in rabbit ventricular myocytes does not alter sarcoplasmic reticulum Ca transport

2009 ◽  
Vol 296 (3) ◽  
pp. H698-H703 ◽  
Author(s):  
Jason R. Waggoner ◽  
Kenneth S. Ginsburg ◽  
Bryan Mitton ◽  
Kobra Haghighi ◽  
Jeffrey Robbins ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Mammalian Species ◽  
Cardiac Contractility ◽  
Adult Rabbit ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Important Species ◽  
Plasmic Reticulum ◽  
Rabbit Ventricular Myocytes ◽  
Serca 2A

Phospholamban has been suggested to be a key regulator of cardiac sarcoplasmic reticulum (SR) Ca cycling and contractility and a potential therapeutic target in restoring the depressed Ca cycling in failing hearts. Our understanding of the function of phospholamban stems primarily from studies in genetically altered mouse models. To evaluate the significance of this protein in larger mammalian species, which exhibit Ca cycling properties similar to humans, we overexpressed phospholamban in adult rabbit cardiomyocytes. Adenoviral-mediated gene transfer, at high multiplicities of infection, resulted in an insignificant 1.22-fold overexpression of phospholamban. There were no effects on twitch Ca-transient amplitude or decay under basal or isoproterenol-stimulated conditions. Furthermore, the SR Ca load and Na/Ca exchanger function were not altered. These apparent differences between phospholamban overexpression in rabbit compared with previous findings in the mouse may be due to a significantly higher (1.5-fold) endogenous phospholamban-to-sarco(endo)plasmic reticulum Ca-ATPase (SERCA) 2a ratio and potential functional saturation of SERCA2a by phospholamban in rabbit cardiomyocytes. The findings suggest that important species-dependent differences in phospholamban regulation of SERCA2a occur. In larger mammals, a higher fraction of SERCA2a pumps are regulated by phospholamban, and this may influence therapeutic strategies to enhance cardiac contractility and functional cardiac reserve.

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