Variable Titin-Based Stiffness Adjustment in Heart Disease

To the Editor: Several issues in a previous letter to the Editor1 concerning our work on titin in heart disease require clarification. We have studied titin isoform expression in the canine pacing model of heart failure2 and found that in controls, stiff (N2B) and compliant (N2BA) cardiac titin isoforms are coexpressed at ≈1:1 ratio, whereas after pacing, the stiff isoform is upregulated at the expense of the more compliant one.2 Using skinned muscle strips dissected from the midwall region of the left ventricle (LV) (note that we …