The effects of β-adrenergic stimulation on phospholamban phosphorylation and Ca 2+-ATPase activity were studied in intact myocarduim. Isolated guinea pig ventricles were perfused via the coronary arteries with 32P(i) after which membrane vesicles, comprised primarily of sarcoplasmic reticulum, were isolated by differential centrifugation. Isoproterenol perfusion increased 32P incorporation into membrane proteins of apparent M(r)=22.000 and 8,000, which have been shown to be the predominant proteins phosphorylated in sarcoplasmic reticulum by cAMP-dependent protein kinase. 32P incorporation was increased 3.8-fold and 7.1-fold after 60-s exposure to 10 and 100 nM isoproterenol, respectively. In the same membrane vesicles, Ca 2+-ATPase activity was increased by 30 and 52%, respectively. The increases in phospholamban phosphorylation and Ca 2+-ATPase activity correlated in time and concentration dependence with increases in the rate of myocardial relaxation. These biochemical changes did not correlate well with positive inotropy. Similar effects were produced by histamine, 1μM. The onset of the effects of isoproterenol on phospholamban phosphorylation and Ca 2+-ATPase activity closely paralleled the relaxation effects. However, reversal of the relaxant effects occurred more rapidly than the return of 32P incorporation and Ca 2+-ATPase activity to control levels. These results provide evidence that β-adrenergic stimulation results in phospholamban phosphorylation and increased Ca 2+-ATPase activity in intact, functioning ventricular myocardium. These findings support the hypothesis that stimulation of sarcoplasmic reticulum Ca 2+ transport, mediated by cAMP-dependent phosphorylation of phospolamban, may underlie the relaxant effects of β-adrenergic stimulation in mammalian myocardium.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - Sep 8 1983|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology