Myosin light chain composition in non-failing donor and end-stage failing human ventricular myocardium.

The increased Ca(2+)-responsiveness in end-stage human heart failure cannot be attributed to contractile protein isoform changes, but rather is the complex resultant of changes in degree of phosphorylation of VLC-2 and TnI. Despite the decreased basal level of VLC-2 phosphorylation the response to VLC-2 dephosphorylation is enhanced in failing myocytes, which might result from differences in endogenous phosphorylation of thin and thick filament proteins between donor and failing hearts. Taken together decreased VLC-2 phosphorylation in end-stage human heart failure might represent a compensatory process leading to an improvement of myocardial contractility by opposing the detrimental effects of increased Ca(2+)-responsiveness of force and impaired Ca(2+)-handling on diastolic function.