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Protein kinase C modulation of the regulation of sarcoplasmic reticular function by protein kinase A‐mediated phospholamban phosphorylation in diabetic rats
Author(s) -
Watanuki Satoko,
Matsuda Naoyuki,
Sakuraya Fumika,
Jesmin Subrina,
Hattori Yuichi
Publication year - 2004
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0705455
Subject(s) - phospholamban , medicine , endocrinology , protein kinase c , protein kinase a , phosphorylation , endoplasmic reticulum , protein phosphorylation , isoprenaline , biology , chemistry , stimulation , biochemistry
The goal of this study was to elucidate the possible mechanisms by which protein kinase A (PKA)‐mediated regulation of the sarcoplasmic reticulum (SR) via phospholambin protein phosphorylation is functionally impaired in streptozotocin‐induced diabetic rats. Phospholamban (PLB) protein and mRNA levels were 1.3‐fold higher in diabetic than in control hearts, while protein expression of cardiac SR Ca 2+ ‐ATPase (SERCA2a) was unchanged. Basal and isoprenaline‐stimulated phosphorylation of PLB at Ser 16 or Thr 17 was unchanged in diabetic hearts. However, stronger immunoreactivity was observed at the basal level in diabetic hearts when antiphosphoserine antibody was used. Basal 32 P incorporation into PLB was significantly higher in diabetic than in control SR vesicles, but the extent of the PKA‐mediated increase in PLB phosphorylation was the same in the two groups of vesicles. Stimulation of Ca 2+ uptake by PKA‐catalyzed PLB phosphorylation was weaker in diabetic than in control SR vesicles. The PKA‐induced increase in Ca 2+ uptake was attenuated when control SR vesicles were preincubated with protein kinase C (PKC). PKC activities were increased by more than two‐fold in the membranous fractions from diabetic hearts in comparison with control values, regardless of whether Ca 2+ was present. This was associated with increases in the protein content of PKC δ , PKC η , PKC ι , and PKC λ in diabetic membranous fractions. The changes observed in diabetic rats were reversed by insulin therapy. These results suggest that PKA‐dependent phosphorylation may incompletely counteract the function of PLB as an inhibitor of SERCA2a activity in diabetes in which PKC expression and activity are enhanced.British Journal of Pharmacology (2004) 141 , 347–359. doi: 10.1038/sj.bjp.0705455