Frequency dependent force generation correlates with sarcoplasmic calcium ATPase activity in human myocardium.
OBJECTIVE
In congestive heart failure both a decreased function of the sarcoplasmic Ca(2+)-ATPase and a negative force-frequency relationship have been shown. This study aimed to investigate a possible relationship between frequency potentiation, sarcoplasmic Ca(2+)-ATPase activity, and SERCA2 protein expression in human myocardium.


METHODS
Frequency potentiation was studied in electrically stimulated, isometric, left ventricular papillary muscle strip preparations (37 degrees C, 0.5-3.0 Hz) from terminally failing (NYHA i.v.; n = 5, dilated cardiomyopathy) and nonfailing (donor hearts, n = 5) human myocardium. In the identical samples the Ca(2+)-ATPase activity (NADH coupled assay) and the protein expression of sarcoplasmic Ca(2+)-ATPase (SERCA2), phospholamban, and calsequestrin (western blot) were determined. The frequency dependent change in the force of contraction and Vmax of the Ca(2+)-ATPase activity and the protein expression of SERCA2 were correlated with each other.


RESULTS
In terminally failing myocardium the force-frequency relationship was negative (2.0 Hz vs. 0.5 Hz: -0.2 +/- 0.1 delta mN) contrasting a positive rate dependent potentiation of force in nonfailing tissue (2.0 Hz vs. 0.5 Hz: +0.8 +/- 0.2 delta mN; p < 0.01). In failing myocardium the corresponding maximal sarcoplasmic Ca(2+)-ATPase activity (Vmax) was reduced significantly compared to nonfailing myocardium (174 +/- 24 vs. 296 +/- 31 nmol ATP/mg.min, p < 0.01). The protein expression of SERCA2, phospholamban, and calsequestrin remained unchanged in failing myocardium. The maximal Ca(2+)-ATPase activity significantly correlated with the frequency dependent change in force of contraction (2 Hz vs. 0.5 Hz: r = 0.88, p = 0.001; 3 Hz vs. 0.5 Hz: r = 0.84, p = 0.004). No correlation between protein expression of SERCA2 and Ca(2+)-ATPase activity or change in force of contraction was observed.


CONCLUSIONS
Due to a significant correlation between sarcoplasmic Ca(2+)-ATPase activity and frequency potentiation, the negative rate dependent force potentiation in human heart failure could be at least in part be attributed to decreased function of the sarcoplasmic Ca(2+)-ATPase.
Frank
K
K
Klinik III für Innere Medizin der Universität zu Köln.
Bölck
B
B
Bavendiek
U
U
Schwinger
R H
RH
D000328:Adult; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000378:metabolism*; D002155:Calsequestrin / Q000032:analysis / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D006333:Heart Failure / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000166:cytology / Q000201:enzymology; D009206:Myocardium / Q000737:chemistry / Q000166:cytology / Q000201:enzymology*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D016277:Ventricular Function, Left; D000099211:Phospholamban
D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D002155:Calsequestrin; D000099211:Phospholamban