Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8473396 | Journal of Molecular and Cellular Cardiology | 2018 | 30 Pages |
Abstract
Changes in the nonischemic remote myocardium of the heart contribute to left ventricular dysfunction after ischemia and reperfusion (I/R). Understanding the underlying mechanisms early after I/R is crucial to improve the adaptation of the viable myocardium to increased mechanical demands. Here, we investigated the role of myocyte Ca2+ handling in the remote myocardium 24â¯h after 60â¯min LAD occlusion. Cardiomyocytes isolated from the basal noninfarct-related parts of wild type mouse hearts demonstrated depressed beat-to-beat Ca2+ handling. The amplitude of the Ca2+ transients as well as the kinetics of Ca2+ transport were reduced by up to 25%. These changes were associated with impaired sarcomere contraction. While expression levels of Ca2+ regulatory proteins were unchanged in remote myocardium compared to the corresponding regions of sham-operated hearts, mobility shift analyses of phosphorylated protein showed 2.9â¯Â±â¯0.4-fold more unphosphorylated phospholamban (PLN) monomers, the PLN species that inhibits the Ca2+ ATPase SERCA2a (Pâ¯â¤â¯0.001). Phospho-specific antibodies revealed normal phosphorylation of PLN at T17 in remote myocardium, but markedly reduced phosphorylation at its PKA-dependent phosphorylation site, S16 (Pâ¯â¤â¯0.01). The underlying cause involved enhanced activity of protein phosphatases, particularly PP2A (Pâ¯â¤â¯0.01). In contrast, overall PKA activity was normal. The PLN interactome, as determined by co-immunoprecipitation and mass spectrometry, and the phosphorylation state of PKA targets other than PLN were also unchanged. Isoproterenol enhanced cellular Ca2+ cycling much stronger in remote myocytes than in healthy controls and improved sarcomere function. We conclude that the reduced phosphorylation state of PLN at S16 impairs myocyte Ca2+ cycling in the remote myocardium 24â¯h after I/R and contributes to contractile dysfunction.
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Authors
Annette Kronenbitter, Florian Funk, Katarzyna Hackert, Simone GorreÃen, Dennis Glaser, Peter Boknik, Gereon Poschmann, Kai Stühler, Malgorzata IsiÄ, Martina Krüger, Joachim P. Schmitt,