Differential Changes in Cardiac Phospholamban and Sarcoplasmic Reticular Ca 2+ -ATPase Protein Levels

Abstract

Abstract The objective of this study was to elucidate the role of the sarcoplasmic reticulum (SR) in the transition from compensated pressure-overload hypertrophy (increased left ventricular [LV] mass, normal LV function, and no pulmonary congestion) to congestive heart failure (increased LV mass, depressed LV function, and pulmonary congestion). To address this issue, the descending thoracic aorta was banded for 4 and 8 weeks in adult guinea pigs, and the changes in isovolumic LV mechanics, SR Ca 2+ transport, and SR protein levels were determined and compared with age-matched sham-operated control animals. A subgroup of the 8-week banded animals manifested the congestive heart failure phenotype with diminished developed LV pressure normalized by LV mass, reduced rates of LV pressure development and relaxation, and markedly increased lung weight–to–body weight ratios. The cardiac mechanical and morphometric changes were associated with depressed protein levels of the SR Ca 2+ -ATPase (85% of the control) and phospholamban (65% of the control) assessed by quantitative immunoblotting. Resultant rates of SR Ca 2+ uptake (V max ) and the affinity of SR Ca 2+ -ATPase for Ca 2+ (EC 50 ) were significantly depressed [32±6 nmol Ca 2+ · min −1 · mg −1 and 0.59±0.12 (μmol/L)/L, respectively] compared with the 8-week sham-operated control animals [40±1 nmol Ca 2+ · min −1 · mg −1 and 0.40±0.05 (μmol/L)/L, respectively]. We conclude that this model of pressure overload–induced cardiac failure is associated with (1) diminished LV force development, rates of pressure development, and decay; (2) depressed protein expression of the Ca 2+ -cycling proteins SR Ca 2+ -ATPase and phospholamban; and (3) decreased V max and affinity of the SR Ca 2+ -ATPase for Ca 2+ . These findings implicate these Ca 2+ -cycling proteins in the pathogenesis of congestive heart failure.