Publication Detail

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Cardiac SR-coupled PP1 activity and expression are increased and inhibitor 1 protein expression is decreased in failing hearts.

Ramesh C Gupta; Sudhish Mishra; Sharad Rastogi; Makoto Imai; Omar Habib; Hani N Sabbah (Profiled Author: Hani N Sabbah)

Division of Cardiovascular Medicine, Department of Medicine, Henry Ford Heart and Vascular Institute, Detroit, MI 48202, USA. rgupta1@hfhs.org
American journal of physiology. Heart and circulatory physiology 2003;285(6):H2373-81.

Type 1 protein phosphatase (PP1) is a negative regulator of cardiac function. However, studies on the status and regulation of sarcoplasmic reticulum (SR)-associated PP1 activity in failing hearts are limited. We studied PP1 activity and protein and mRNA expression of the catalytic subunit of PP1 (PP1C) and protein levels of PP1-specific inhibitors [inhibitor 1 (Inh-1) and inhibitor 2 (Inh-2)] in the left ventricular (LV) myocardium of 6 dogs with heart failure (HF; LV ejection fraction, 23 +/- 2%) and 6 normal dogs. In failing LV tissue, PP1 activity values (expressed as pmol 32P. min-1. mg of noncollagen protein-1) in the homogenate, crude membranes, cytosol, and purified SR were increased by 52, 54, 55, and 72%, respectively. Trypsin treatment released PP1 but not type 2A protein phosphatase from the SR. In the supernatant of trypsin-treated SR, PP1 activity was approximately 24% higher in failing hearts than in normal control hearts. A similar increase in protein expression of PP1C was observed in the nontrypsinized SR. Heat-denatured phosphorylated SR inhibited PP1 activity by 30%, which suggests the presence of Inh-1 or -2 or both in the SR. With the use of a specific antibody, both Inh-1 and -2 proteins were found in the SR; the former was decreased by 56% in the failing SR, whereas the latter did not change. These results suggest that protein phosphatase activity bound to the SR is increased and is predominantly type 1. Increased SR-associated PP1 activity in failing hearts appears to be due partly to increased expression of PP1C and partly to reduced levels of Inh-1 but not Inh-2 protein. Thus inhibition of PP1 activity in the SR appears to be a potential therapeutic target for improving LV function in failing hearts, because it may lead to increased SR Ca2+ uptake, which is impaired in failing hearts.

1 Originating Grant

• 1.

  Sabbah, Hani N

  PROGRESSION OF HEART FAILURE

  1 April 1994 - 31 December 2003

  NATIONAL HEART, LUNG, AND BLOOD INSTITUTE

  Total Funding: $ 2,329,997

Scientific Context

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