We tested the hypothesis that the negative functional effects of cyclic GMP on cardiac myocytes were mediated through phospholamban (PLB) and activation of sarcoplasmic reticulum Ca 2+ -ATPase. Using ventricular myocytes from wild type (WT, n=10) and PLB knockout (PLB-KO, n=10) mouse hearts, functional changes were measured using a video edge detector at baseline and after 10 -6 , 10 -5 M 8-bromo-cyclic GMP (cGMP), 10 -8 , 10 -7 M C-type natriuretic peptide (CNP), or 10 -6 , 10 -5 M S-nitroso-N-acetyl-penicillamine (SNAP, nitric oxide donor). Changes in cytosolic Ca 2+ concentration were assessed in fura 2-loaded WT and PLB-KO myocytes. Cyclic GMP dependent phosphorylation analysis was also performed in WT and PLB-KO myocytes. 8-bromo-cGMP 10 -5 M caused a significant decrease in %shortening (3.6±0.2% to 2.3±0.1%) in WT, but little change in PLB-KO myocytes (3.4±0.1% to 3.2±0.2%). Similarly, CNP and SNAP reduced %shortening of WT, but not PLB-KO myocyte. Changes in other contractile parameters such as maximum rate of shortening and relaxation were consistent with the changes in % shortening. Intracellular Ca 2+ transients changed similarly to cell contractility in WT and PLB-KO myocytes treated with cGMP and CNP; i.e. Ca 2+ transients decreased with cGMP or CNP in WT myocytes, but were unchanged in PLB-KO myocytes. cGMP dependent phosphorylation analysis showed that some proteins were phosphorylated by cGMP to a lesser extent in PLB-KO compared with WT myocytes, suggesting impaired cGMP-kinase function in PLB-KO cardiac myocytes. These results indicated that cGMP-induced reductions in cardiac myocyte function were at least partially mediated through the action of phospholamban.
All Science Journal Classification (ASJC) codes
- Cardiac myocyte function
- Cyclic GMP
- Natriuretic peptides
- Nitric oxide